Inflammatory recruitment of leukocytes is governed by dynamic interactions between integrins and endothelial immunoglobulin superfamily (IgSF) proteins. We have identified the IgSF member junctional adhesion molecule 1 (JAM-1) as a ligand of the β₂ integrin lymphocyte function–associated antigen 1 (LFA-1). Under static and physiological flow conditions, JAM-1 contributed to LFA-1–dependent transendothelial migration of T cells and neutrophils as well as LFA-1–mediated arrest of T cells. The latter was triggered by chemokines on endothelium that was stimulated with cytokines to redistribute JAM-1 from the tight junctions. Transfectants expressing JAM-1 supported LFA-1–mediated adhesion of leukocytes, which required the membrane-proximal Ig-like domain 2 of JAM-1. Thus, JAM-1 is a counter-receptor for LFA-1 that is ideally situated to guide and control transmigration during leukocyte recruitment.