The article reviews the effects, sources, and fate of extracellular ATP (adenosine triphosphate). ATP, a ubiquitous intracellular component, can be released into the extracellular milieu from various cell types, including purinergic nerve terminals, blood cells, and other cells. This release can occur through exocytosis or active transport mechanisms. Extracellular ATP can influence a wide range of biological processes, such as platelet aggregation, vascular tone, neurotransmission, cardiac function, and muscle contraction. The article discusses the classification of purinoceptors, which are receptors that recognize ATP and ADP, and highlights the differences between P1 and P2 receptors. P2 receptors are more responsive to ATP and ADP than to AMP and adenosine and are not blocked by methylxanthines. The article also explores the sources of extracellular ATP, including purinergic nerve terminals, blood cells, and other cells, and the mechanisms by which ATP is released. Additionally, it covers the metabolism of ATP, which is efficiently removed by ectonucleotidases in the lungs and blood, and the role of ectonucleotidases in regulating the concentrations of circulating vasoactive purines. The article concludes by emphasizing the diverse and significant regulatory roles of extracellular ATP in various physiological and pathological contexts.The article reviews the effects, sources, and fate of extracellular ATP (adenosine triphosphate). ATP, a ubiquitous intracellular component, can be released into the extracellular milieu from various cell types, including purinergic nerve terminals, blood cells, and other cells. This release can occur through exocytosis or active transport mechanisms. Extracellular ATP can influence a wide range of biological processes, such as platelet aggregation, vascular tone, neurotransmission, cardiac function, and muscle contraction. The article discusses the classification of purinoceptors, which are receptors that recognize ATP and ADP, and highlights the differences between P1 and P2 receptors. P2 receptors are more responsive to ATP and ADP than to AMP and adenosine and are not blocked by methylxanthines. The article also explores the sources of extracellular ATP, including purinergic nerve terminals, blood cells, and other cells, and the mechanisms by which ATP is released. Additionally, it covers the metabolism of ATP, which is efficiently removed by ectonucleotidases in the lungs and blood, and the role of ectonucleotidases in regulating the concentrations of circulating vasoactive purines. The article concludes by emphasizing the diverse and significant regulatory roles of extracellular ATP in various physiological and pathological contexts.