Some cameras have the ability to store data directly off the sensor and into a file that contains extra color information; this is commonly referred to as 'RAW' or 'camera RAW', and Shotwell supports these files as well.
Since RAW photographs normally cannot be displayed directly, but must be first developed - that is, have their extra information interpreted and readied for displaying - most cameras will either embed a JPEG inside a RAW-format file, or produce a JPEG alongside the RAW file at the time the snapshot is taken. The latter is referred to throughout this document as RAW+JPEG. If you import a RAW+JPEG pair, Shotwell will keep them paired and treat them as one item in your library.
When you import a RAW file, you can choose to either use the camera's internally-developed JPEG or Shotwell's by selecting Photos ▸ Developer in the menus.
Changing between developers will cause all edits made to a photograph to be discarded.
In order to publish or use a RAW photograph in most other software, it has to be exported first. Shotwell can export your RAW photos in JPEG, PNG, TIFF or BMP format, and, when publishing, will internally export a JPEG version for you and publish that.