P2Y receptors are G-protein-coupled receptors (GPCRs) for extracellular nucleotides. There are eight mammalian P2Y receptor subtypes (P2Y₁, P2Y₂, P2Y₄, P2Y₆, P2Y₁₁, P2Y₁₂, P2Y₁₃, and P2Y₁₄). The widely expressed P2Y receptors play important roles in physiology and pathophysiology. This review summarizes the use of pharmacological tools to characterize the P2Y receptor subtypes involved in these responses. MRS2500 is a potent and selective antagonist acting at the P2Y₁ receptor. AR-C118925 is useful for the selective antagonism of the P2Y₂ receptor. PSB16133 blocks the P2Y₄ receptor, MRS2578 is an antagonist at the P2Y₆ receptor and NF157 as well as NF340 block the P2Y₁₁ receptor. ADP-induced platelet aggregation is mediated by P2Y₁ and P2Y₁₂ receptors. A number of compounds or their active metabolites reduce ADP-induced platelet aggregation by blocking the P2Y₁₂ receptor. These include the active metabolites of the thienopyridine compounds clopidogrel and prasugrel, the nucleoside analogue ticagrelor and the nucleotide analogue cangrelor. PSB0739 is also a potent antagonist at the P2Y₁₂ receptor useful for both in vitro and in vivo studies. MRS2211 and MRS2603 inhibit P2Y₁₃ mediated responses. PPTN is a very potent antagonist at the P2Y₁₄ receptor.