Integrins are transmembrane receptors that facilitate cell-extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, organization of the intracellular cytoskeleton, and movement of new receptors to the cell membrane. The presence of integrins allow rapid and flexible responses to events at the cell surface (i.e. signal platelets to initiate an interaction with coagulation factors).

Several types of integrins exist, and one cell may have multiple different types on its surface. Integrins are found in all animals.

Integrins work alongside other receptors such as cadherins, the immunoglobulin superfamily cell adhesion molecules, selectins and syndecans to mediate cell–cell and cell–matrix interaction. Ligands for integrins include fibronectin, vitronectin, collagen and laminin.

Integrins are obligate heterodimers, meaning that they have two subunits: α (alpha) and β (beta). Integrins in mammals have eighteen α and eight β subunits, in Drosophila five α and two β subunits, and in Caenorhabditis nematodes two α subunits and one β subunit. The α and β subunits each penetrate the plasma membrane and possess small cytoplasmic domains.

Variants of some subunits are formed by differential RNA splicing; for example, four variants of the beta-1 subunit exist. Through different combinations of the α and β subunits, around 24 unique integrins are generated.

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