Physiological, pharmacological and molecular biological data generated over the past three decades have demonstrated the existence of two major families of extracellular receptors, the P1, a family of four G-protein coupled receptors and the P2, a family of at least 12 receptors responsive to purine (ATP, ADP) and pyrimidine (UTP) nucleotides through which adenosine and ATP can function as extracellular messengers. The present two-part volume represents an integrated compendium of invited chapters by leading researchers in the area focusing on advances in the understanding of purinergic and pyrimidinergic signaling systems, their role(s) in tissue function and pathophysiology and advances in developing potential new medications based on the modulation of P1 and P2 receptor signaling processes. The volumes will thus provide the reader with a topical, comprehensive and integrated overview of this important area.