The invention relates to a camshaft adjuster (1) for adjusting and fixing the relative position of the angle of rotation of a camshaft (8) in relation to a crankshaft of a reciprocating piston internal combustion engine. The adjusting device comprises a high transmission and friction-reduced adjusting gear mechanism (2), comprising a drive shaft which is rotationally fixed to the crankshaft, a driven shaft which is rotationally fixed to the camshaft (8) and an adjusting shaft (9) which is connected to an adjusting motor shaft (10) of an adjusting motor. A camshaft adjuster (1), which is economical to run, can be produced such that the adjusting gear mechanism (2) and the adjusting motor (3) are embodied as separate units and are connected together by a rotational backlash-free, disengaging coupling (4).