The cadherins are transmembrane glycoproteins involved in calcium dependent specific cell-cell adhesion through homophilic binding. They are crucial for morphogenesis and synapse formation, but also are involved in tumor invasion. The classical cadherins have five homologous extracellular domains and a cytosolic domain which binds through catenin to the cytoskeleton. The extracellular domains are immunoglobulin-like beta-sandwiches comprising usually 7 strands in the two sheets.