Calcium/calmodulin dependent serine protein kinase (CASK), which belongs to the family of membrane associated guanylate kinase (MAGUK) proteins, has several isoforms. CASK expresses differently in embryonic tissues and adult tissues. It can be modulated by phosphorylation and SUMOylation. CASK plays an important role in neural development, spermatozoal development and renal development. Dysfunction of CASK may lead to diseases. CASK is distributed extensively in the brain, regulating synapse formation. Mutation of CASK can lead to several neurologic diseases. CASK is also involved in the development and maturation of sperm and fertilization. It also can influence renal development through interaction with DLG1.