Windows Photo Viewer (formerly Windows Picture and Fax Viewer) is an image viewer included with the Windows NT family of operating systems. It was first included with Windows XP and Windows Server 2003 under its former name, succeeding Imaging for Windows. It was removed in Windows Vista and was replaced with Windows Photo Gallery, but was reinstated in Windows 7 under its current name.

Windows Photo Viewer can show individual pictures, display all pictures in a folder as a slide show, reorient them in 90° increments, print them either directly or via an online print service, send them in e-mail or burn them to a disc. Windows Photo Viewer supports images in BMP, JPEG, JPEG XR (formerly HD Photo), PNG, ICO, GIF and TIFF file formats.

Windows Photo Viewer is deprecated in Windows 10 and later in favor of a Universal Windows Platform app called Photos. The program can no longer be accessed by normal means, however it can be re-enabled by editing the registry.

Windows Picture and Fax Viewer allows images to be displayed without opening them up in an image editor. It uses GDI+ and can display a variety of image file formats, including animated GIFs, as well as displaying slide shows of images. Images can be zoomed in and out without any additional modifications to the image file, and can be rotated with changes saved directly to the file when closing the image viewer. Windows Picture and Fax Viewer can also annotate TIFF files, and can even view and edit multi-page TIFF files, however TIFF files with JPEG compression is not fully supported.

Unlike with Imaging for Windows, Windows Picture and Fax Viewer does not include the advanced features of said application.

Compared to Windows Picture and Fax Viewer, changes have been made to the graphical user interface in Windows Photo Viewer. Whereas Windows Picture and Fax Viewer uses GDI+, Windows Photo Viewer uses Windows Imaging Component (WIC) and takes advantage of Windows Display Driver Model.

Although GIF files are supported in Windows Photo Viewer, Windows Photo Viewer only displays the first frame of the animated GIF whereas Windows Picture and Fax Viewer displays animated GIFs in full. Windows Picture and Fax Viewer was also capable of viewing multi-page TIFF files (except those that employ JPEG compression) as well as annotating the TIFF files, whereas Windows Photo Viewer cannot, though it does handle multi-page WEBP files. On the other hand, Windows Photo Viewer has added support for JPEG XR and ICC Profiles (Windows Picture and Fax Viewer also has support for ICC Profiles but only for v2).

Some devices and Android phones are able to take photos and screenshots and have a custom ICC Profile being applied to said pictures, however Windows Photo Viewer will display an error when trying to display the picture with the message "Windows Photo Viewer can't display this picture because there might not be enough memory available on your computer" when an unknown ICC Profile is detected. There is a patch available on GitHub that fixes this behavior. Also, when a custom Display ICC Profile is applied after installing a Monitor driver, Windows Photo Viewer wrongly shifts the picture hue to a warm tint. This feature is intentional but is greatly exaggerated. This can be fixed by removing or replacing the Display ICC Profile.