In cellular biology, cell–cell recognition is a cell's ability to distinguish one type of neighboring cell from another. This phenomenon occurs when complementary molecules on opposing cell surfaces meet. A receptor on one cell surface binds to its specific ligand on a nearby cell, initiating a cascade of events which regulate cell behaviors ranging from simple adhesion to complex cellular differentiation. Like other cellular functions, cell–cell recognition is impacted by detrimental mutations in the genes and proteins involved and is subject to error. The biological events that unfold due to cell–cell recognition are important for animal development, microbiomes, and human medicine.