Cylindrical lenses are optical lenses which are curved only in one direction. Therefore, they focus or defocus light only in one direction, for example in the horizontal direction but not in the vertical direction. As for ordinary lenses, their focusing or defocusing behavior can be characterized with a focal length or its inverse, the dioptric power.

Usually, the surface curvature of a cylindrical lens is of spherical type, but there are also aspheric cylindrical lenses. Further, there are cylindrical gradient-index lenses, not exhibiting any surface curvature.