Merlin is a unique protein. Both involved in the regulation of the cell cycle as a suppressor of tumorigenesis as well as in the formation of cytoskeletal structures. The structure is distinguished by merlin FERM globular domain occurring in many families of proteins of different functions and the helical C-terminal fragment. Merlin activity is controlled transitions between open and closed form, wherein the FERM domain interacts with the C-terminal fragment. Merlin in the form of an open participates in interactions with many proteins adhesion, structural and regulatory, and closed form of the protein CD44, which probably determines its tumor suppressor properties. The mechanism involving the suppression of merlin is still unclear. The proposed models have implicated merlin in creating a feedback loop of small GTPases signaling pathway and involved in contact inhibition.