Decorin is a secreted chondroitin/dermatan sulfate proteoglycan in the family of small leucine-rich proteoglycans (SLRPs). SLRP family members are characterized by N-terminal and C-terminal cysteine-rich regions which flank the central region containing 10-12 tandem leucine-rich repeats (LRR). The human Decorin cDNA encodes a 359 amino acid (aa) precursor that includes a 16 aa signal sequence and a 14 aa propeptide. Alternate splicing of human Decorin generates five isoforms with variable length deletions. Decorin is an N-glycosylated protein that also carries a variablysized hybrid chondroitin/dermatan sulfate chain at Ser34. Decorin regulates assembly of the extracellular collagen matrix and the bioactivity of the matrix associated growth factors FGF2,GDF8/Myostatin, TGFβ,and WISP1. It also binds and activates EGF R, ErbB4, and IGFI-R. In vivo, Decorin promotes myoblast differentiation, supports angiogenesis, and inhibits tumor progression.