Obesity, a major threat to global human health, has been shown to be associated with devastating diseases such as stroke, hypertension, cancer and type 2 diabetes. In order to fight the present obesity pandemic it is crucial to better understand regulation of adipocyte differentiation. Phosphodiesterases (PDEs) catalyze hydrolysis of cyclic nucleotides (cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP)) to the corresponding 5′ nucleotide monophosphates. To date, eleven different PDEs (PDE1–11) have been characterized, and they differ in their selectivity for cyclic nucleotides, sensitivity to inhibitors and activators, physiological roles, and tissue distribution. The nonselective phosphodiesterase inhibitor isobutylmethylxanthine (IBMX) has been shown to be essential for successful in vitro differentiation of adipocytes.