Endoglin (CD105) is a type III receptor for the transforming growth factor beta (TGFβ) superfamily that plays important role in hematopoiesis, angiogenesis, cardiovascular development, and vascular remodeling. Endoglin is a 180 kD homodimeric integral membrane glycoprotein composed of disulfide-linked subunits. Endoglin is composed of 561 amino acid extracellular domain, a transmembrane domain, and a 47 amino acid cytoplasmic domain (L-endoglin). An isoform with a 14 amino acid domain (S-endoglin) can oppose effects of L-endoglin. The extracellular domain of endoglin can be proteolytically cleaved by matrix metalloproteinase 14 and released as soluble endoglin. Endoglin is highly expressed in vascular endothelial cells, chondrocytes, placental syncytiotrophoblasts, stromal cells of mesenchymal origin, smooth muscle cells, hematopoietic and mesenchymal stem cells, activated monocytes, and leukemic cells of lymphoid and myeloid lineage. Endoglin can be found in the receptor complex for the TGFβ1 and TGFβ3 isoforms in association with the type II receptor. Endoglin interacts with activin, BMP2 and BMP7 in association with their ligand binding receptors. Endoglin also directly binds with BMP9 and BMP10. Deletion of mouse Endoglin causes lethal vascular and cardiovascular defects, and human Endoglin haploinsufficiency can cause the vascular disorder and hereditary hemorrhagic telangiectasia type I. Soluble endoglin contributes to the pathogenesis of preeclampsia.