An overview of platelet receptor–ligand interactions. Platelets express various receptors for agonists or integrins and glycoproteins for ligands. The receptor–ligand interactions play critical roles in platelet activation, aggregation, shape change, adhesion, and thrombus formation. Green circle: integrins and glycoproteins for platelet adhesion and aggregation; blue circle: platelet receptors for agonists; orange circle: integrins and lectins for platelet–cell interaction; rectangle with gray line: endogenous ligands or agonists for each receptor. Abbreviations: PAR1, protease activated receptor 1; P2RY12, P2Y purinoceptor 12; TP, thromboxane receptor; 5-HT2AR, 5-hydroxytryptamine (serotonin) receptor 2A; CLEC-2, C-type lectin-like receptor 2; VWF, von Willebrand factor; PSGL-1, P-selectin glycoprotein ligand-1.