Non-selective inhibitors of cyclic nucleotide phosphodiesterase (PDE), such as theophylline, have been used extensively since 1958. In the decade of the '70s, various PDE isoenzymes were defined which led to the development of the second generation of PDE inhibitors. Currently a variety of these new inhibitors are under test as potential anti-inflammatory drugs. During the past five years, molecular biology has revealed a superfamily of these phosphodiesterase isoenzymes. This book summarizes the present state of knowledge, as well as giving a comprehensive description of the compounds available. It will be invaluable for everyone who wants to choose the most suitable PDE inhibitor for their research or who is dealing with such drugs in a clinical setting.