Channel 4 (previously 4oD and All 4) is a video on demand service from Channel Four Television Corporation, free of charge for most content and funded by advertising. The service is available in the UK and Ireland; viewers are not required to have a TV licence—required for live viewing and the BBC iPlayer on-demand service—when watching on-demand services.

The service offers a variety of programmes recently shown on Channel 4, E4, More4, Film4 and E4 Extra and shorts, alongside exclusive content such as programming from Adult Swim. However some programmes and movies are not available due to rights issues. The service was originally available without registration, but free registration was later required. The service is available without advertising (except for live viewing) on payment of a subscription, under the name Channel 4+ (previously All 4+).

The service launched on 16 November 2006 as 4oD (for "4 on Demand"). All 4 generated around 215 million long-form video views on all platforms where it is available in the first half of 2011, making Channel 4 the biggest commercial UK broadcaster in the video on-demand market during the period. On 30 March 2015, 4oD was merged into and renamed All 4. (References below to "All 4" before that date should be understood as including 4oD.) On 28 February 2019, All 4 was rebranded with a new logo, website design and app design. On 17 April 2023, All 4 rebranded as Channel 4, becoming the "first UK broadcaster to adopt one brand identity across its digital and linear channels".

All 4 is the main source of on demand programmes from Channel 4, E4, and More4. The catch up service currently lasts 30 days, and the archive has thousands of hours of programming.

By April 2009, the Internet version was fully available to Mac and Windows users with Adobe Flash Player installed.

The "catch-up" service offers content free of charge for 30 days after a programme's broadcast on Channel 4. As of 2011, not all content is available to Irish users, due to licensing restrictions; however, the majority of the programming is available. Live streaming of Channel 4 and its sister channels is not available outside the UK.

Channel 4 relaunched 4oD on 31 August 2011. At the heart of the changes is 'My 4oD', allowing registered users to build playlists, schedule shows, maintain a record of what they have watched, save their favourites in a single place, and receive in-page reminders from Channel 4 whenever a new episode is available for them to watch. Other features include better full-page viewing and optimised site navigation during viewing.

Since 2014, the service stops users with ad blocking software from watching videos on All 4.^{[citation needed]}