Adenosine is a nucleoside formed when adenine is attached to a ribose ring (also known as a ribofuranose) via a β-N9-glycosidic bond.

Adenosine plays an important role in biochemical processes, such as energy transfer - as adenosine triphosphate (ATP) and adenosine diphosphate (ADP) - as well as in signal transduction as cyclic adenosine monophosphate, cAMP.

If adenine is attached to a deoxyribose ring, it is known as a deoxyadenosine.