diff --git src/wp-admin/includes/image-edit.php src/wp-admin/includes/image-edit.php
index 0430dbefbf..52b403d180 100644
--- src/wp-admin/includes/image-edit.php
+++ src/wp-admin/includes/image-edit.php
@@ -306,6 +306,12 @@ function wp_stream_image( $image, $mime_type, $attachment_id ) {
 			case 'image/gif':
 				header( 'Content-Type: image/gif' );
 				return imagegif( $image );
+			case 'image/webp':
+				if ( function_exists( 'imagewebp' ) ) {
+					header( 'Content-Type: image/webp' );
+					return imagewebp( $image, null, 90 );
+				}
+				return false;
 			default:
 				return false;
 		}
@@ -391,6 +397,11 @@ function wp_save_image_file( $filename, $image, $mime_type, $post_id ) {
 				return imagepng( $image, $filename );
 			case 'image/gif':
 				return imagegif( $image, $filename );
+			case 'image/webp':
+				if ( function_exists( 'imagewebp' ) ) {
+					return imagewebp( $image, $filename );
+				}
+				return false;
 			default:
 				return false;
 		}
diff --git src/wp-admin/includes/image.php src/wp-admin/includes/image.php
index 673c1dff01..142c245f89 100644
--- src/wp-admin/includes/image.php
+++ src/wp-admin/includes/image.php
@@ -517,6 +517,9 @@ function wp_generate_attachment_metadata( $attachment_id, $file ) {
 				case 'image/png':
 					$ext = '.png';
 					break;
+				case 'image/webp':
+					$ext = '.webp';
+					break;
 			}
 			$basename = str_replace( '.', '-', wp_basename( $file ) ) . '-image' . $ext;
 			$uploaded = wp_upload_bits( $basename, '', $metadata['image']['data'] );
@@ -913,7 +916,7 @@ function file_is_valid_image( $path ) {
  * @return bool True if suitable, false if not suitable.
  */
 function file_is_displayable_image( $path ) {
-	$displayable_image_types = array( IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG, IMAGETYPE_BMP, IMAGETYPE_ICO );
+	$displayable_image_types = array( IMAGETYPE_GIF, IMAGETYPE_JPEG, IMAGETYPE_PNG, IMAGETYPE_BMP, IMAGETYPE_ICO, IMAGETYPE_WEBP ); // phpcs:ignore PHPCompatibility.Constants.NewConstants.imagetype_webpFound
 
 	$info = wp_getimagesize( $path );
 	if ( empty( $info ) ) {
@@ -963,6 +966,12 @@ function load_image_to_edit( $attachment_id, $mime_type, $size = 'full' ) {
 		case 'image/gif':
 			$image = imagecreatefromgif( $filepath );
 			break;
+		case 'image/webp':
+			$image = false;
+			if ( function_exists( 'imagecreatefromwebp' ) ) {
+				$image = imagecreatefromwebp( $filepath );
+			}
+			break;
 		default:
 			$image = false;
 			break;
diff --git src/wp-admin/includes/media.php src/wp-admin/includes/media.php
index 14a8d99b49..bdfb65d103 100644
--- src/wp-admin/includes/media.php
+++ src/wp-admin/includes/media.php
@@ -993,7 +993,7 @@ function wp_media_upload_handler() {
 function media_sideload_image( $file, $post_id = 0, $desc = null, $return = 'html' ) {
 	if ( ! empty( $file ) ) {
 
-		$allowed_extensions = array( 'jpg', 'jpeg', 'jpe', 'png', 'gif' );
+		$allowed_extensions = array( 'jpg', 'jpeg', 'jpe', 'png', 'gif', 'webp' );
 
 		/**
 		 * Filters the list of allowed file extensions when sideloading an image from a URL.
diff --git src/wp-admin/includes/schema.php src/wp-admin/includes/schema.php
index a59c7c36ce..6f528f2288 100644
--- src/wp-admin/includes/schema.php
+++ src/wp-admin/includes/schema.php
@@ -1215,6 +1215,7 @@ We hope you enjoy your new site. Thanks!
 		'jpeg',
 		'png',
 		'gif',
+		'webp',
 		// Video.
 		'mov',
 		'avi',
diff --git src/wp-includes/class-wp-image-editor-gd.php src/wp-includes/class-wp-image-editor-gd.php
index ed0a7be279..42a8929ff8 100644
--- src/wp-includes/class-wp-image-editor-gd.php
+++ src/wp-includes/class-wp-image-editor-gd.php
@@ -69,6 +69,8 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 				return ( $image_types & IMG_PNG ) != 0;
 			case 'image/gif':
 				return ( $image_types & IMG_GIF ) != 0;
+			case 'image/webp':
+				return ( $image_types & IMG_WEBP ) != 0; // phpcs:ignore PHPCompatibility.Constants.NewConstants.img_webpFound
 		}
 
 		return false;
@@ -99,7 +101,15 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 			return new WP_Error( 'error_loading_image', __( 'File doesn’t exist?' ), $this->file );
 		}
 
-		$this->image = @imagecreatefromstring( $file_contents );
+		// WebP may not work with imagecreatefromstring().
+		if (
+			function_exists( 'imagecreatefromwebp' ) &&
+			( 'image/webp' === wp_get_image_mime( $this->file ) )
+		) {
+			$this->image = @imagecreatefromwebp( $this->file );
+		} else {
+			$this->image = @imagecreatefromstring( $file_contents );
+		}
 
 		if ( ! is_gd_image( $this->image ) ) {
 			return new WP_Error( 'invalid_image', __( 'File is not an image.' ), $this->file );
@@ -459,6 +469,10 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 			if ( ! $this->make_image( $filename, 'imagejpeg', array( $image, $filename, $this->get_quality() ) ) ) {
 				return new WP_Error( 'image_save_error', __( 'Image Editor Save Failed' ) );
 			}
+		} elseif ( 'image/webp' == $mime_type ) {
+			if ( ! function_exists( 'imagewebp' ) || ! $this->make_image( $filename, 'imagewebp', array( $image, $filename, $this->get_quality() ) ) ) {
+				return new WP_Error( 'image_save_error', __( 'Image Editor Save Failed' ) );
+			}
 		} else {
 			return new WP_Error( 'image_save_error', __( 'Image Editor Save Failed' ) );
 		}
@@ -502,6 +516,12 @@ class WP_Image_Editor_GD extends WP_Image_Editor {
 			case 'image/gif':
 				header( 'Content-Type: image/gif' );
 				return imagegif( $this->image );
+			case 'image/webp':
+				if ( function_exists( 'imagewebp' ) ) {
+					header( 'Content-Type: image/webp' );
+					return imagewebp( $this->image, null, $this->get_quality() );
+				}
+				// Fall back to the default if webp isn't supported.
 			default:
 				header( 'Content-Type: image/jpeg' );
 				return imagejpeg( $this->image, null, $this->get_quality() );
diff --git src/wp-includes/class-wp-image-editor-imagick.php src/wp-includes/class-wp-image-editor-imagick.php
index e4f1ea1b16..36a344b15b 100644
--- src/wp-includes/class-wp-image-editor-imagick.php
+++ src/wp-includes/class-wp-image-editor-imagick.php
@@ -197,19 +197,30 @@ class WP_Image_Editor_Imagick extends WP_Image_Editor {
 		}
 
 		try {
-			if ( 'image/jpeg' === $this->mime_type ) {
-				$this->image->setImageCompressionQuality( $quality );
-				$this->image->setImageCompression( imagick::COMPRESSION_JPEG );
-			} else {
-				$this->image->setImageCompressionQuality( $quality );
+			switch ( $this->mime_type ) {
+				case 'image/jpeg':
+					$this->image->setImageCompressionQuality( $quality );
+					$this->image->setImageCompression( imagick::COMPRESSION_JPEG );
+					break;
+				case 'image/webp':
+					if ( _wp_webp_is_lossy( $this->file ) ) {
+						$this->image->setImageCompressionQuality( $quality );
+					} else {
+						// Use WebP lossless settings.
+						$this->image->setImageCompressionQuality( 100 );
+						$this->image->setOption( 'webp:lossless', 'true' );
+					}
+					break;
+				default:
+					$this->image->setImageCompressionQuality( $quality );
 			}
 		} catch ( Exception $e ) {
 			return new WP_Error( 'image_quality_error', $e->getMessage() );
 		}
-
 		return true;
 	}
 
+
 	/**
 	 * Sets or updates current image size.
 	 *
diff --git src/wp-includes/class-wp-theme.php src/wp-includes/class-wp-theme.php
index d9ccf6b6ba..b365f45715 100644
--- src/wp-includes/class-wp-theme.php
+++ src/wp-includes/class-wp-theme.php
@@ -1141,7 +1141,7 @@ final class WP_Theme implements ArrayAccess {
 			return false;
 		}
 
-		foreach ( array( 'png', 'gif', 'jpg', 'jpeg' ) as $ext ) {
+		foreach ( array( 'png', 'gif', 'jpg', 'jpeg', 'webp' ) as $ext ) {
 			if ( file_exists( $this->get_stylesheet_directory() . "/screenshot.$ext" ) ) {
 				$this->cache_add( 'screenshot', 'screenshot.' . $ext );
 				if ( 'relative' === $uri ) {
diff --git src/wp-includes/compat.php src/wp-includes/compat.php
index 7f6c59f03c..59e5700439 100644
--- src/wp-includes/compat.php
+++ src/wp-includes/compat.php
@@ -370,3 +370,11 @@ if ( ! function_exists( 'is_iterable' ) ) {
 		return ( is_array( $var ) || $var instanceof Traversable );
 	}
 }
+
+// WebP constants may not be defined, even in cases where the format is supported.
+if ( ! defined( 'IMAGETYPE_WEBP' ) ) {
+	define( 'IMAGETYPE_WEBP', 18 );
+}
+if ( ! defined( 'IMG_WEBP' ) ) {
+	define( 'IMG_WEBP', IMAGETYPE_WEBP ); // phpcs:ignore PHPCompatibility.Constants.NewConstants.imagetype_webpFound
+}
diff --git src/wp-includes/customize/class-wp-customize-media-control.php src/wp-includes/customize/class-wp-customize-media-control.php
index d327a4fa38..22bf75dad5 100644
--- src/wp-includes/customize/class-wp-customize-media-control.php
+++ src/wp-includes/customize/class-wp-customize-media-control.php
@@ -91,7 +91,7 @@ class WP_Customize_Media_Control extends WP_Customize_Control {
 				// Fake an attachment model - needs all fields used by template.
 				// Note that the default value must be a URL, NOT an attachment ID.
 				$ext  = substr( $this->setting->default, -3 );
-				$type = in_array( $ext, array( 'jpg', 'png', 'gif', 'bmp' ), true ) ? 'image' : 'document';
+				$type = in_array( $ext, array( 'jpg', 'png', 'gif', 'bmp', 'webp' ), true ) ? 'image' : 'document';
 
 				$default_attachment = array(
 					'id'    => 1,
diff --git src/wp-includes/deprecated.php src/wp-includes/deprecated.php
index 72a23cd836..2c5f24bde0 100644
--- src/wp-includes/deprecated.php
+++ src/wp-includes/deprecated.php
@@ -3340,6 +3340,8 @@ function gd_edit_image_support($mime_type) {
 				return (imagetypes() & IMG_PNG) != 0;
 			case 'image/gif':
 				return (imagetypes() & IMG_GIF) != 0;
+			case 'image/webp':
+				return (imagetypes() & IMG_WEBP) != 0; // phpcs:ignore PHPCompatibility.Constants.NewConstants.img_webpFound
 		}
 	} else {
 		switch( $mime_type ) {
@@ -3349,6 +3351,8 @@ function gd_edit_image_support($mime_type) {
 				return function_exists('imagecreatefrompng');
 			case 'image/gif':
 				return function_exists('imagecreatefromgif');
+			case 'image/webp':
+				return function_exists('imagecreatefromwebp');
 		}
 	}
 	return false;
diff --git src/wp-includes/formatting.php src/wp-includes/formatting.php
index b716c6bc1f..8dda8c738d 100644
--- src/wp-includes/formatting.php
+++ src/wp-includes/formatting.php
@@ -3318,7 +3318,7 @@ function translate_smiley( $matches ) {
 
 	$matches    = array();
 	$ext        = preg_match( '/\.([^.]+)$/', $img, $matches ) ? strtolower( $matches[1] ) : false;
-	$image_exts = array( 'jpg', 'jpeg', 'jpe', 'gif', 'png' );
+	$image_exts = array( 'jpg', 'jpeg', 'jpe', 'gif', 'png', 'webp' );
 
 	// Don't convert smilies that aren't images - they're probably emoji.
 	if ( ! in_array( $ext, $image_exts, true ) ) {
diff --git src/wp-includes/functions.php src/wp-includes/functions.php
index 56d5fd9f43..3bb257ab8b 100644
--- src/wp-includes/functions.php
+++ src/wp-includes/functions.php
@@ -2886,6 +2886,7 @@ function wp_check_filetype_and_ext( $file, $filename, $mimes = null ) {
 					'image/gif'  => 'gif',
 					'image/bmp'  => 'bmp',
 					'image/tiff' => 'tif',
+					'image/webp' => 'webp',
 				)
 			);
 
@@ -3063,6 +3064,35 @@ function wp_get_image_mime( $file ) {
 		} else {
 			$mime = false;
 		}
+
+		if ( false !== $mime ) {
+			return $mime;
+		}
+
+		$handle = fopen( $file, 'rb' );
+		if ( false === $handle ) {
+			return false;
+		}
+
+		$magic = fread( $handle, 12 );
+		if ( false === $magic ) {
+			return false;
+		}
+
+		// Add WebP fallback detection when image library doesn't support WebP.
+		// Note: detection values come from LibWebP, see
+		// https://github.com/webmproject/libwebp/blob/master/imageio/image_dec.c#L30
+		$magic = bin2hex( $magic );
+		if (
+			// RIFF.
+			( 0 === strpos( $magic, '52494646' ) ) &&
+			// WEBP.
+			( 16 === strpos( $magic, '57454250' ) )
+		) {
+			$mime = 'image/webp';
+		}
+
+		fclose( $handle );
 	} catch ( Exception $e ) {
 		$mime = false;
 	}
@@ -3101,6 +3131,7 @@ function wp_get_mime_types() {
 			'png'                          => 'image/png',
 			'bmp'                          => 'image/bmp',
 			'tiff|tif'                     => 'image/tiff',
+			'webp'                         => 'image/webp',
 			'ico'                          => 'image/x-icon',
 			'heic'                         => 'image/heic',
 			// Video formats.
@@ -3222,7 +3253,7 @@ function wp_get_ext_types() {
 	return apply_filters(
 		'ext2type',
 		array(
-			'image'       => array( 'jpg', 'jpeg', 'jpe', 'gif', 'png', 'bmp', 'tif', 'tiff', 'ico', 'heic' ),
+			'image'       => array( 'jpg', 'jpeg', 'jpe', 'gif', 'png', 'bmp', 'tif', 'tiff', 'ico', 'heic', 'webp' ),
 			'audio'       => array( 'aac', 'ac3', 'aif', 'aiff', 'flac', 'm3a', 'm4a', 'm4b', 'mka', 'mp1', 'mp2', 'mp3', 'ogg', 'oga', 'ram', 'wav', 'wma' ),
 			'video'       => array( '3g2', '3gp', '3gpp', 'asf', 'avi', 'divx', 'dv', 'flv', 'm4v', 'mkv', 'mov', 'mp4', 'mpeg', 'mpg', 'mpv', 'ogm', 'ogv', 'qt', 'rm', 'vob', 'wmv' ),
 			'document'    => array( 'doc', 'docx', 'docm', 'dotm', 'odt', 'pages', 'pdf', 'xps', 'oxps', 'rtf', 'wp', 'wpd', 'psd', 'xcf' ),
diff --git src/wp-includes/media.php src/wp-includes/media.php
index f5b6a39968..82d1b32627 100644
--- src/wp-includes/media.php
+++ src/wp-includes/media.php
@@ -4980,6 +4980,7 @@ function wp_show_heic_upload_error( $plupload_settings ) {
  * Allows PHP's getimagesize() to be debuggable when necessary.
  *
  * @since 5.7.0
+ * @since 5.8.0 Added support for WebP images.
  *
  * @param string $filename   The file path.
  * @param array  $image_info Optional. Extended image information (passed by reference).
@@ -4994,9 +4995,9 @@ function wp_getimagesize( $filename, array &$image_info = null ) {
 		defined( 'WP_DEBUG' ) && WP_DEBUG
 	) {
 		if ( 2 === func_num_args() ) {
-			return getimagesize( $filename, $image_info );
+			return _wp_get_image_size( $filename, $image_info );
 		} else {
-			return getimagesize( $filename );
+			return _wp_get_image_size( $filename );
 		}
 	}
 
@@ -5011,9 +5012,133 @@ function wp_getimagesize( $filename, array &$image_info = null ) {
 	 */
 	if ( 2 === func_num_args() ) {
 		// phpcs:ignore WordPress.PHP.NoSilencedErrors
-		return @getimagesize( $filename, $image_info );
+		return @_wp_get_image_size( $filename, $image_info );
 	} else {
 		// phpcs:ignore WordPress.PHP.NoSilencedErrors
-		return @getimagesize( $filename );
+		return @_wp_get_image_size( $filename );
 	}
 }
+
+/**
+ * Extracts meta information about a webp file: width, height and type.
+ *
+ * @since 5.8.0
+ *
+ * @param [type] $filename Path to a WebP file.
+ * @return array $webp_info {
+ *     An array of WebP image information.
+ *
+ *     @type array $size {
+ *         @type int  $width  Image width.
+ *         @type int  $height Image height.
+ *         @type bool $type   The WebP type: one of 'lossy', 'lossless' or 'animated-alpha'.
+ *     }
+ */
+function wp_get_webp_info( $filename ) {
+	$width  = false;
+	$height = false;
+	$type   = false;
+	if ( ! 'image/webp' === wp_get_image_mime( $filename ) ) {
+		return compact( 'width', 'height', 'type' );
+	}
+	try {
+		$handle = fopen( $filename, 'rb' );
+		if ( $handle ) {
+			$magic = fread( $handle, 40 );
+			fclose( $handle );
+
+			// Make sure we got enough bytes.
+			if ( strlen( $magic ) < 40 ) {
+				return compact( 'width', 'height', 'type' );
+			}
+
+			// The headers are a little different for each of the three formats.
+			// Header values based on WebP docs, see https://developers.google.com/speed/webp/docs/riff_container.
+			switch ( substr( $magic, 12, 4 ) ) {
+				// Lossy WebP.
+				case 'VP8 ':
+					$parts  = unpack( 'v2', substr( $magic, 26, 4 ) );
+					$width  = (int) ( $parts[1] & 0x3FFF );
+					$height = (int) ( $parts[2] & 0x3FFF );
+					$type   = 'lossy';
+					break;
+				// Lossless WebP.
+				case 'VP8L':
+					$parts  = unpack( 'C4', substr( $magic, 21, 4 ) );
+					$width  = (int) ( $parts[1] | ( ( $parts[2] & 0x3F ) << 8 ) ) + 1;
+					$height = (int) ( ( ( $parts[2] & 0xC0 ) >> 6 ) | ( $parts[3] << 2 ) | ( ( $parts[4] & 0x03 ) << 10 ) ) + 1;
+					$type   = 'lossless';
+					break;
+				// Animated/alpha WebP.
+				case 'VP8X':
+					// Pad 24-bit int.
+					$width = unpack( 'V', substr( $magic, 24, 3 ) . "\x00" );
+					$width = (int) ( $width[1] & 0xFFFFFF ) + 1;
+					// Pad 24-bit int.
+					$height = unpack( 'V', substr( $magic, 27, 3 ) . "\x00" );
+					$height = (int) ( $height[1] & 0xFFFFFF ) + 1;
+					$type   = 'animated-alpha';
+					break;
+			}
+		}
+	} catch ( Exception $e ) {
+	}
+	return compact( 'width', 'height', 'type' );
+}
+
+/**
+ * Determines if a passed image is a lossy WebP image.
+ *
+ * @since 5.8.0
+ *
+ * @param string $filename The file path.
+ * @return bool Whether the file is a lossy WebP file.
+ */
+function _wp_webp_is_lossy( $filename ) {
+	$webp_info = wp_get_webp_info( $filename );
+	$type      = $webp_info['type'];
+	return $type && 'lossy' === $type;
+}
+
+/**
+ * Gets the image size, with support for WebP images.
+ *
+ * @since 5.8.0
+ * @access private
+ *
+ * @param string $filename  The file path.
+ * @param array  $imageinfo Extended image information, passed by reference.
+ * @return array|false Array of image information or false on failure.
+ */
+function _wp_get_image_size( $filename, &$imageinfo = array() ) {
+	// Try getimagesize() first.
+	$info = getimagesize( $filename, $imageinfo );
+	if ( false !== $info ) {
+		return $info;
+	}
+	// For PHP versions that don't support WebP images, extract the image
+	// size info from the file headers.
+	if ( 'image/webp' === wp_get_image_mime( $filename ) ) {
+		$webp_info = wp_get_webp_info( $filename );
+		$width     = $webp_info['width'];
+		$height    = $webp_info['height'];
+
+			// Mimic the native return format.
+		if ( $width && $height ) {
+			return array(
+				$width,
+				$height,
+				IMAGETYPE_WEBP, // phpcs:ignore PHPCompatibility.Constants.NewConstants.imagetype_webpFound
+				sprintf(
+					'width="%d" height="%d"',
+					$width,
+					$height
+				),
+				'mime' => 'image/webp',
+			);
+		}
+	}
+
+	// The image could not be parsed.
+	return false;
+}
diff --git src/wp-includes/post.php src/wp-includes/post.php
index abf6f1df46..56cd4a8cd5 100644
--- src/wp-includes/post.php
+++ src/wp-includes/post.php
@@ -6539,7 +6539,7 @@ function wp_attachment_is( $type, $post = null ) {
 
 	switch ( $type ) {
 		case 'image':
-			$image_exts = array( 'jpg', 'jpeg', 'jpe', 'gif', 'png' );
+			$image_exts = array( 'jpg', 'jpeg', 'jpe', 'gif', 'png', 'webp' );
 			return in_array( $ext, $image_exts, true );
 
 		case 'audio':
diff --git src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
index ea4ae947cc..007cee774b 100644
--- src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
+++ src/wp-includes/rest-api/endpoints/class-wp-rest-attachments-controller.php
@@ -438,7 +438,7 @@ class WP_REST_Attachments_Controller extends WP_REST_Posts_Controller {
 			);
 		}
 
-		$supported_types = array( 'image/jpeg', 'image/png', 'image/gif' );
+		$supported_types = array( 'image/jpeg', 'image/png', 'image/gif', 'image/webp' );
 		$mime_type       = get_post_mime_type( $attachment_id );
 		if ( ! in_array( $mime_type, $supported_types, true ) ) {
 			return new WP_Error(
diff --git tests/phpunit/data/images/test-image.webp tests/phpunit/data/images/test-image.webp
new file mode 100644
index 0000000000..37ab153807
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diff --git tests/phpunit/data/images/webp-lossless.webp tests/phpunit/data/images/webp-lossless.webp
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diff --git tests/phpunit/data/images/webp-lossy.webp tests/phpunit/data/images/webp-lossy.webp
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diff --git tests/phpunit/data/images/webp-transparent.webp tests/phpunit/data/images/webp-transparent.webp
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diff --git tests/phpunit/tests/functions.php tests/phpunit/tests/functions.php
index f485d3b4ec..a088db940e 100644
--- tests/phpunit/tests/functions.php
+++ tests/phpunit/tests/functions.php
@@ -1225,6 +1225,29 @@ class Tests_Functions extends WP_UnitTestCase {
 		$this->assertSame( $expected, wp_get_image_mime( $file ) );
 	}
 
+	/**
+	 * @ticket 35725
+	 * @dataProvider data_wp_getimagesize
+	 */
+	public function test_wp_getimagesize( $file, $expected ) {
+		if ( ! is_callable( 'exif_imagetype' ) && ! function_exists( 'getimagesize' ) ) {
+			$this->markTestSkipped( 'The exif PHP extension is not loaded.' );
+		}
+
+		$result = wp_getimagesize( $file );
+
+		// The getimagesize() function varies in its response, so
+		// let's restrict comparison to expected keys only.
+		if ( is_array( $expected ) ) {
+			foreach ( $expected as $k => $v ) {
+				$this->assertEquals( true, isset( $result[ $k ] ) );
+				$this->assertEquals( $expected[ $k ], $result[ $k ] );
+			}
+		} else {
+			$this->assertEquals( $expected, $result );
+		}
+	}
+
 	/**
 	 * @ticket 39550
 	 * @dataProvider _wp_check_filetype_and_ext_data
@@ -1313,6 +1336,129 @@ class Tests_Functions extends WP_UnitTestCase {
 				DIR_TESTDATA . '/images/test-image-mime-jpg.png',
 				'image/jpeg',
 			),
+			// Animated WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-animated.webp',
+				'image/webp',
+			),
+			// Lossless WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-lossless.webp',
+				'image/webp',
+			),
+			// Lossy WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-lossy.webp',
+				'image/webp',
+			),
+			// Transparent WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-transparent.webp',
+				'image/webp',
+			),
+			// Not an image.
+			array(
+				DIR_TESTDATA . '/uploads/dashicons.woff',
+				false,
+			),
+		);
+
+		return $data;
+	}
+
+	/**
+	 * Data profider for test_wp_getimagesize();
+	 */
+	public function data_wp_getimagesize() {
+		$data = array(
+			// Standard JPEG.
+			array(
+				DIR_TESTDATA . '/images/test-image.jpg',
+				array(
+					50,
+					50,
+					IMAGETYPE_JPEG,
+					'width="50" height="50"',
+					'mime' => 'image/jpeg',
+				),
+			),
+			// Standard GIF.
+			array(
+				DIR_TESTDATA . '/images/test-image.gif',
+				array(
+					50,
+					50,
+					IMAGETYPE_GIF,
+					'width="50" height="50"',
+					'mime' => 'image/gif',
+				),
+			),
+			// Standard PNG.
+			array(
+				DIR_TESTDATA . '/images/test-image.png',
+				array(
+					50,
+					50,
+					IMAGETYPE_PNG,
+					'width="50" height="50"',
+					'mime' => 'image/png',
+				),
+			),
+			// Image with wrong extension.
+			array(
+				DIR_TESTDATA . '/images/test-image-mime-jpg.png',
+				array(
+					50,
+					50,
+					IMAGETYPE_JPEG,
+					'width="50" height="50"',
+					'mime' => 'image/jpeg',
+				),
+			),
+			// Animated WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-animated.webp',
+				array(
+					100,
+					100,
+					IMAGETYPE_WEBP,
+					'width="100" height="100"',
+					'mime' => 'image/webp',
+				),
+			),
+			// Lossless WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-lossless.webp',
+				array(
+					1200,
+					675,
+					IMAGETYPE_WEBP,
+					'width="1200" height="675"',
+					'mime' => 'image/webp',
+				),
+			),
+			// Lossy WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-lossy.webp',
+				array(
+					1200,
+					675,
+					IMAGETYPE_WEBP,
+					'width="1200" height="675"',
+					'mime' => 'image/webp',
+				),
+			),
+			// Transparent WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-transparent.webp',
+				array(
+					1200,
+					675,
+					IMAGETYPE_WEBP,
+					'width="1200" height="675"',
+					'mime' => 'image/webp',
+				),
+			),
 			// Not an image.
 			array(
 				DIR_TESTDATA . '/uploads/dashicons.woff',
diff --git tests/phpunit/tests/image/editor.php tests/phpunit/tests/image/editor.php
index 47ee30a658..dce95ee836 100644
--- tests/phpunit/tests/image/editor.php
+++ tests/phpunit/tests/image/editor.php
@@ -195,4 +195,84 @@ class Tests_Image_Editor extends WP_Image_UnitTestCase {
 
 		$this->assertSame( '100x50', $editor->get_suffix() );
 	}
+
+	/**
+	 * Test wp_get_webp_info.
+	 *
+	 * @ticket 35725
+	 * @dataProvider _test_wp_get_webp_info
+	 *
+	 */
+	public function test_wp_get_webp_info( $file, $expected ) {
+		$editor = wp_get_image_editor( $file );
+		if ( is_wp_error( $editor ) || ! $editor->supports_mime_type( 'image/webp' ) ) {
+			$this->markTestSkipped( sprintf( 'Skipping test: no WebP support in the editor engine %s on this system.', $this->editor_engine ) );
+		} else {
+			$file_data = wp_get_webp_info( $file );
+			$this->assertSame( $file_data, $expected );
+		}
+	}
+
+	/**
+	 * Data provider for test_wp_get_webp_info();
+	 */
+	public function _test_wp_get_webp_info() {
+		return array(
+			// Standard JPEG.
+			array(
+				DIR_TESTDATA . '/images/test-image.jpg',
+				array(
+					'width'  => false,
+					'height' => false,
+					'type'   => false,
+				),
+			),
+			// Standard GIF.
+			array(
+				DIR_TESTDATA . '/images/test-image.gif',
+				array(
+					'width'  => false,
+					'height' => false,
+					'type'   => false,
+				),
+			),
+			// Animated WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-animated.webp',
+				array(
+					'width'  => 100,
+					'height' => 100,
+					'type'   => 'animated-alpha',
+				),
+			),
+			// Lossless WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-lossless.webp',
+				array(
+					'width'  => 1200,
+					'height' => 675,
+					'type'   => 'lossless',
+				),
+			),
+			// Lossy WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-lossy.webp',
+				array(
+					'width'  => 1200,
+					'height' => 675,
+					'type'   => 'lossy',
+				),
+			),
+			// Transparent WebP.
+			array(
+				DIR_TESTDATA . '/images/webp-transparent.webp',
+				array(
+					'width'  => 1200,
+					'height' => 675,
+					'type'   => 'animated-alpha',
+				),
+			),
+		);
+	}
+
 }
diff --git tests/phpunit/tests/image/functions.php tests/phpunit/tests/image/functions.php
index 1694c1e7f1..0658e45117 100644
--- tests/phpunit/tests/image/functions.php
+++ tests/phpunit/tests/image/functions.php
@@ -59,6 +59,10 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			'test-image.psd',
 			'test-image-zip.tiff',
 			'test-image.jpg',
+			'webp-animated.webp',
+			'webp-lossless.webp',
+			'webp-lossy.webp',
+			'webp-transparent.webp',
 		);
 
 		// IMAGETYPE_ICO is only defined in PHP 5.3+.
@@ -92,6 +96,21 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			'test-image.jpg',
 		);
 
+		// Add WebP images if the image editor supports them.
+		$file   = DIR_TESTDATA . '/images/test-image.webp';
+		$editor = wp_get_image_editor( $file );
+		if ( ( ! is_wp_error( $editor ) ) && $editor->supports_mime_type( 'image/webp' ) ) {
+			$files = array_merge(
+				$files,
+				array(
+					'webp-animated.webp',
+					'webp-lossless.webp',
+					'webp-lossy.webp',
+					'webp-transparent.webp',
+				)
+			);
+		}
+
 		// IMAGETYPE_ICO is only defined in PHP 5.3+.
 		if ( defined( 'IMAGETYPE_ICO' ) ) {
 			$files[] = 'test-image.ico';
@@ -174,6 +193,11 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			'image/png',
 		);
 
+		// Include WebP in tests when platform supports it.
+		if ( function_exists( 'imagewebp' ) ) {
+			array_push( $mime_types, 'image/webp' );
+		}
+
 		// Test each image editor engine.
 		foreach ( $classes as $class ) {
 			$img    = new $class( DIR_TESTDATA . '/images/canola.jpg' );
@@ -270,7 +294,8 @@ class Tests_Image_Functions extends WP_UnitTestCase {
 			'jpe'  => 'image/jpeg',
 			'gif'  => 'image/gif',
 			'png'  => 'image/png',
-			'unk'  => 'image/jpeg', // Default, unknown.
+			'webp' => 'image/webp',
+			'unk'  => 'image/jpeg',   // Default, unknown.
 		);
 
 		// Test each image editor engine.
diff --git tests/phpunit/tests/image/resize.php tests/phpunit/tests/image/resize.php
index 3e3255e6a5..517ab45389 100644
--- tests/phpunit/tests/image/resize.php
+++ tests/phpunit/tests/image/resize.php
@@ -64,6 +64,24 @@ abstract class WP_Tests_Image_Resize_UnitTestCase extends WP_Image_UnitTestCase
 		unlink( $image );
 	}
 
+	function test_resize_webp() {
+		$file   = DIR_TESTDATA . '/images/test-image.webp';
+		$editor = wp_get_image_editor( $file );
+
+		// Check if the editor supports the webp mime type.
+		if ( is_wp_error( $editor ) || ! $editor->supports_mime_type( 'image/webp' ) ) {
+			$this->markTestSkipped( sprintf( 'Skipping test: no WebP support in the editor engine %s on this system.', $this->editor_engine ) );
+		} else {
+			$image = $this->resize_helper( $file, 25, 25 );
+			$this->assertSame( 'test-image-25x25.webp', wp_basename( $image ) );
+			list($w, $h, $type) = wp_getimagesize( $image );
+			$this->assertSame( 25, $w );
+			$this->assertSame( 25, $h );
+			$this->assertSame( IMAGETYPE_WEBP, $type );
+			unlink( $image );
+		}
+	}
+
 	function test_resize_larger() {
 		// image_resize() should refuse to make an image larger.
 		$image = $this->resize_helper( DIR_TESTDATA . '/images/test-image.jpg', 100, 100 );