Adenosine is a ubiquitous adenine base purine that mediates diverse biological and physiological processes in the cardiovascular system, both in cardiac and vascular tissues. Adenosine was reported to be involved in smooth muscle contraction, neurotransmission/neuromodulation, immune response and inflammation, platelet aggregation and modulation of cardiac function. Adenosine availability, in the extracellular space, depends on its release from a variety of cell types, as a result of adenosine triphosphate (ATP) enzymatic breakdown of both intra- and extracellular adenine nucleotides and intracellular S-adenosylhomocysteine. This book discusses the pharmacology, functions and therapeutic aspects of adenosine receptors.