Is Leica M9 a SLR?

M9 can change lenses, as long as it is an M-port lens or an old L39-port lens with a ring, it can be used on Leica's M-series fuselage.

M9 is not a SLR camera, but a paraxial camera (viewing by axis and linkage ranging). Leica is the first brand in the world to invent 135 camera. At that time, there was no SLR at all, and Leica was the only brand in the world that insisted on making paraxial cameras from beginning to end (Leica R series SLR was sometimes just for fun).

SLR is the product of fast photography and documentary photography, because what you see is what you get. Paraaxis is the product of serious photography and humanistic photography, because what you can't see is what you get, and every link in the photography process needs your own operation. Don't buy M9 if you haven't played sideline. Shooting with a viewfinder is what you see is what you get, which requires a lot of experience and calculation. Without a few years of photography experience, the rejection rate is high.

Basically, people who play photography are degraded to some extent. More than 90% of professional photographers will eventually have a Leica and nothing else.