Phosphodiesterases (PDEs) are a superfamily of enzymes that degrade cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). There are now 11 PDE families identified, many of which exist as splice variants. PDEs influence a number of pharmacological processes, including proinflammatory mediator production and action, ion channel function, muscle contraction, learning, differentiation, apoptosis, lipogenesis, glycogenolysis, and gluconeogenesis.