Spatial and temporal compartmentalization of cAMP (and its target proteins) is central to the ability of this second messenger to govern cellular activity over timescales ranging from milliseconds to several hours. Recent years have witnessed a burgeoning of methodologies that enable researchers to directly monitor rapid subcellular cAMP dynamics, which are unobtainable by traditional cAMP assays. In this review, we examine cAMP biosensors that are currently available for measuring cAMP at the single-cell level, compare their various operating principles and discuss their applications.