Research leaders in the PDE field describe new concepts and techniques for investigating the role of PDEs in orchestrating normal and pathophysiological responses. Presented in step-by-step detail, these readily reproducible methods allow the measurement of cyclic nucleotide variations in living cells, as well as their visualization in a spatio-temporal manner, the localization and characterization of their activities in tissues and living cells, and the assessment of targeted PDEs in creating specific tools and drugs. Additional chapters discuss the generation of PDE4 knockout mice to demonstrate not only the potential role of targeted PDEs, but also their use in further studies of the central role of PDE regulation in intracellular signaling control. These techniques offer clinicians a way to find new therapies for numerous pathologies whose molecular origins are unknown and whose treatment is symptomatic. Alterations of intracellular signaling related to PDE deregulation in such pathologies as inflammation, neurodegeneration, and cancer may explain the difficulties observed in their prevention and treatment.