The Leica M9 was released in September 2009 as the first full-frame digital rangefinder, replacing the APS-H M8 and marking the moment digital M photography no longer cropped the classic lens focal lengths.
It uses an 18MP full-frame Kodak KAF-18500 CCD sensor, ISO 80-2500, a 0.68x rangefinder, 2.5in 230k-dot LCD and a 1/4000s shutter in a 585g body. Files are DNG; there is no live view or video.
The M9's CCD is the reason it endures: its colour rendering is widely described as film-like and distinct from later CMOS bodies, which keeps demand steady among photographers chasing that signature look despite the camera's modest specification.
The critical used-market check is the sensor: early M9 sensors suffered corrosion of the cover glass, and value hinges on whether the sensor was replaced with the corrosion-resistant version - ask for the service record. Also check LCD delamination, rangefinder alignment and battery condition.