Mamiya’s manual focus 645 system was introduced in 1975 and was produced until the 645AF supplanted it in 1999.

There are two generations of manual focus 645 cameras. Lenses can be shared between models of different generations, but accessories can only be used with cameras of the same generation. Earlier generation cameras are called M645 and have mainly metal and leatherette exteriors, while later generation M645 Super/Pro cameras have a more plasticky exterior.

Instead of a leaf shutter like other modular SLRs, the Mamiya 645 uses a focal plane shutter. This allows the camera to use faster shutter speed and makes lenses smaller but limits the camera's ability to sync with a flash.