L-selectin, also known as CD62L, is a cell surface glycoprotein that is constitutively expressed in a variety of leukocytes. It is a cell adhesion molecule present in lymphocytes and preimplantation embryos and is a member of the selectin family of proteins. Studies have reported the existence of two forms of soluble L-selectin (sL-Selectin). sL-Selectin is derived from lymphocytes and has a molecular weight of approximately 62 kDa, whereas sL-Selectin derived from neutrophils has a molecular weight of 75-100 kDa. sL-Selectin at high concentrations prevents lymphocytes from binding to the endothelium, suggesting a role for sL-Selectin in regulating cell adhesion in the body. Selectin may play a role in regulating lymphocyte-endothelial binding in vivo. Monitoring serum levels of sL-Selectin may provide more detailed insight into some pathologies such as sepsis and acquired immunodeficiency syndrome (AIDS).