In this talk we introduce the concepts of CD-rings and CD-modules. Let R be a ring and M an R-module. We call R (M), a CD-ring (CD-module) in the case where every (M-)cosingular R-module (in [M]) is discrete. Let R be a ring such that the class of cosingular R-modules is closed under factor modules. It is proved that R is a CD-ring if and only if every cosigular R-module is semisimple. The relations of CD-rings are investigated with GV -rings, SC-rings and CP-rings. Let R be a semilocal ring. It is shown that R is right CD if and only if R is left SC with Soc(RR) essential in RR.
