PSGL-1, a major selectin ligand on leukocytes, binds P-selectin, E-selectin, and L-selectin under flow conditions. PSGL-1 is a sialomucin of 120 kD that forms disulfide-linked (C320) homodimers. These have two subunits each contain two to three N-glycans, which are critical for P-selectin binding. Each subunit consists of an extracellular, transmembrane, and cytoplasmic domain. PSGL-1 is expressed on most peripheral T cells and on some B cells, neutrophils, monocytes, and platelets. PSGL-1 requires N-terminal tyrosine sulfation for high-affinity P-selectin binding. The PSGL-1 cytoplasmic domain binds ERM proteins, thereby linking PSGL-1 to the actin cytoskeleton. Recently, PSGL-1 has been shown to be of key importance for the delivery of tissue factor to sites of thrombosis. Blocking functional PSGL-1 reduces visceral adipose inflammation and ameliorates endothelial dysfunction in atherosclerosis.