Geranylgeranyltransferases (GGTases) are enzymes involved in the prenylation modification of proteins, divided into GGTase-I and GGTase-II types, which are involved in various cellular signaling transduction and protein localization processes. These enzymes are located on the membranes of the endoplasmic reticulum and Golgi apparatus, transferring geranylgeranyl groups to the cysteine residues of target proteins. GGTases are crucial for processes such as cell proliferation, differentiation, membrane attachment, and signal transduction. Members of their family specifically recognize and modify a range of substrate proteins, including small GTPases. Specific expression of their genes and functional mutations can affect cellular behavior, associated with various diseases including cancer and genetic disorders. The activity and regulation of GGTases play an important role in maintaining the balance of the intracellular signaling network.