The potential use of phosphodiesterase 4 (PDE4) inhibitors to treat various inflammatory diseases such as asthma and chronic obstructive pulmonary disease has garnered significant attention from the pharmaceutical industry over the last few years. In contrast, the potential use of PDE4 inhibitors to treat central nervous system disorders, such as major depressive disorders, has received less attention. With a growing body of work linking intracellular signaling pathways such as modulation of the cAMP second messenger system to a positive outcome following antidepressant therapy, the role that PDE4 inhibitors could play in the treatment of mood disorders has become more apparent. The following review examines the promise that PDE4 inhibitors may hold for the treatment of these diseases.