The invention relates to a valve (1, 1a), in particular an expansion valve, for controlling fluid flow, having a valve central housing (10, 10a) having a first and a second opening (12, 12a, 14, 14a) and a valve element (20, 20a) which has a rotationally symmetrical outline and is arranged rotatably within the valve element housing (10, 10a). According to the invention, the valve element (20, 20a) has a cut-out, wherein the cut-out (30, 30a, 30b, 30c) has a variable dimension, and a sub region (32, 32a) of the cutout (30, 30a, 30b, 30c) is formed continuously through the valve element (20, 20a).