A digital camera is an electronic device used to capture and store photographs electronically in a digital format, instead of using photographic film like conventional cameras, or recording images to film or video.

Modern compact digital cameras are typically multifunctional, with some devices capable of recording sound and/or video as well as photographs. In the Western market, digital still cameras now outsell film based 35 mm cameras.

A full frame digital SLR or single-lens reflex camera built for a pre-existing range of photographic lenses that takes full advantage of the image circle of those lenses by having an imager that is the full size of the film frame that the lenses were designed to cover.

It follows from the above definition that these cameras which use a lens mount that was designed for digital SLRs are not full frame cameras. Similarly, a camera using a hypothetical new mount system and featuring a 24mm x 36mm sensor (the size of a 35mm film frame) would not be full frame.

In practice, however, the term is often simply used to mean a camera having a sensor the same size as a full 35mm frame, while the applicability of the term to four thirds system cameras is a matter of much, often heated, debate.

The chief reason that digital SLRs have not been full frame is to do with the cost of producing such large sensors. Most of the semiconductor industry's advances in affordability have been driven by the ability to make circuits smaller and smaller, but an imaging chip must remain large, and such large chips get cheaper only slowly.

The secondary reason is that digital imaging chips tend to have a much narrower range of acceptance angles than film. Thus, the sensor will be less sensitive to light towards the edges of the image circle, where the light rays are likely to be not quite perpendicular. In addition to this, lenses tend to produce poorer results towards the edge of the circle in any case. A smaller image sensor stays within the so-called "sweet spot" of the lens and sensor combination with less difficulty.

While a digital camera for any format could be full frame, in practice most examples produced have been for 35mm format. The first, fairly unsuccessful attempt was by Contax with a Philips sensor; Pentax worked with this sensor as well, producing a prototype MZ-D, but abandoned it before production. Eastman Kodak produced three models of full-frame camera, but all are now discontinued. The company that has had the most success with full-frame sensors is Canon Inc., whose full-frame sensor cameras have been very successful in the high-end professional photography field. Their newly released model, the Canon EOS 5D, seeks to emulate that success for a much lower price band.

As digital cameras became more common, a question many photographers asked was if their film cameras could be converted to digital. The answer was yes and no. For the majority of 35 mm film cameras the answer is no, the reworking and cost would be too great, especially since lens technology has also been evolving. A conversion to digital, to give enough space for the electronics and allow a liquid crystal display for previewing, would require removing the entire back of the camera and replacing it with a custom built digital unit.

Many early professional SLR cameras, such as the NC2000 and the Kodak DCS series, were developed from 35 mm film cameras. The technology of the time, however, meant that rather than being a digital "back" the body was mounted on a large and blocky digital unit, often bigger than the camera portion itself. These were factory built cameras, however, not aftermarket conversions.

One notable exception was a device called the EFS-1, which was developed by Silicon Film from ca. 1998–2001. It was intended to be inserted into a film camera in the place of film, giving the camera a 1.3 MP resolution and a capacity of 24 shots. Units were demonstrated, and in 2002 the company was developing the EFS-10, a 10 MP device that was more a true digital back.

A few 35 mm cameras have had digital backs made by their manufacturer, Leica being a notable example. Medium format and large format cameras (those using film stock greater than 35 mm), have users who are capable of and willing to pay the price a low unit production digital back requires, typically over $10,000. These cameras also tend to be highly modular, with handgrips, film backs, winders, and lenses available separately to fit various needs.

The very large sensor these backs use can lead to enormous image sizes. The largest in early 2006 is the Phaseone's P45 39 MP imageback, creating a single TIFF image of size upto 224.6 MB. Medium format digitals are geared more towards studio and portrait photography than their smaller DSLR counterparts.