There are essentially three types of cameras that can be used for underwater photography - point-and-shoot, full-featured and dSLR (digital single-lens reflex camera).
Point-and-shoot is the simplest and most compact type of underwater camera. These cameras are very easy to use and designed for casual, fun pictures or videos. A camera on your smartphone, for example, falls into this category. With the release of underwater housings, many smartphone models can now be used for taking pictures underwater.
Full-featured cameras bridge the gap between point-and-shoot and dSLRs. They combine the ease of use and more advanced functionality, which makes them very popular among snorkelers and vacationers. Many waterproof cameras fall into this category.
dSLRs – Digital SLR (Single Lens Reflex) cameras are for those who are serious about photography. Some of the benefits of these cameras include a variety of high-quality interchangeable lenses, better sensors, and no shutter lag. Keep in mind though, not all dSLRs are supported with underwater housings, so before selecting the camera, make sure there is a housing available for it.