Tenascins are a family of large multimeric extracellular matrix (ECM) proteins. Vertebrates express four tenascins termed tenascin-C, -R, -X and -W present in their connective tissues. Each tenascin has a specific expression pattern. To the contrary of many other ECM proteins, tenascins promote only weak cell adhesion and do not activate cell spreading. They have been classified as anti-adhesive, adhesion-modulating or even repellent ECM proteins. Tenascin-C and tenascin-R deficient mice show abnormalities in the nervous system and tenascin-C deficient mice, in addition, have defects in several regenerative processes. Mice lacking tenascin-X display hyperelastic skin much like Ehlers Danlos patients with mutations in their tenascin-X gene. Since tenascin-C is highly overexpressed in tumor stroma antibodies against tenascin-C have been used in tumor diagnosis and therapy. Since tenascins are known to influence cell shape, migration and growth they represent good candidate molecules for inclusion in artificial bioengineered tissue implants.