Photo sharing is the publishing or transfer of a user's digital photos online, thus enabling the user to share them with others (whether publicly or privately). This functionality is provided through both websites and applications that facilitate the upload and display of images. The term can also be loosely applied to the use of online photo galleries that are setup and managed by individual users, including photoblogs.

The first photo sharing sites originated during the mid to late 1990s primarily from service providing online ordering of prints (photo-finishing), but many more came into being during the early 2000s with the goal of providing permanent and centralized access to a user's photos, and in some cases video clips too. This has resulted in different approaches to revenue generation and functionality amongst providers.

While photoblogs tend only to display a chronological view of user-selected medium-sized photos, most photo sharing sites provide multiple views (such as thumbnails, and slideshows), the ability to classify photos into albums as well as add annotations (such as captions or "tags") and comments. Some photo sharing sites provide complete online organization tools equivalent to desktop photo-management applications.

Desktop photo-management applications may include their own photo-sharing features or integration with sites for uploading images to them. There are also desktop applications whose sole function is sharing photos, generally using peer-to-peer networking. Basic photo sharing functionality can be found in applications that allow you to email photos, for example by dragging and dropping them into pre-designed templates.

Photo sharing is not confined to the web and personal computers but is also possible from portable devices such as cameraphones, using applications that can automatically transfer photos as you take them, to photo sharing sites and photoblogs, either directly or via MMS. Some cameras now come equipped with wireless networking and similar sharing functionality themselves.