We study how cell–cell recognition arises from protein–protein interactions between cell surface adhesion and receptor proteins. These interactions allow cells to sense, integrate, and respond to signals from their extracellular environment, shaping key processes in the nervous and immune systems. Our work focuses on the molecular logic of these interactions, including how membrane context and spatial organization influence their function. We combine bioinformatic method development with biochemical and biophysical approaches, including X-ray crystallography and cryo-EM, to uncover the structural and mechanistic basis of cell recognition.