ICAM-1 is a cell surface glycoprotein expressed at a low basal level in immune, endothelial (EC) and epithelial cells, but is up-regulated in response to inflammatory stimulation. The function of ICAM-1 has been best studied in leukocyte transendothelial migration (TEM), where ICAM-1 regulates leukocyte rolling and adhesive interactions with the vessel wall, and guides leukocyte crossing of the endothelial layer. More recently, functional studies identified several new roles of ICAM-1 in epithelial injury-resolution responses, innate and adaptive immune responses in inflammation, and tumorigenesis.