Divided into three parts this volume summarizes the most important areas of Cell-Penetrating Peptides (CPP) research . Part one briefly presents the historical background of CPP studies and the classifications of the available CPPs, and then summarizes the approaches for prediction of novel CPPs. Part two mainly describes the methods for studies of "naked" CPPs, that is, CPPs without conjugated cargos. Last but not least part three presents a representative and brief summary of functionality issues of CPPs, both in vitro and in vivo . As a volume in the highly successful Methods in Molecular Biology series, chapters contain introductions to their respective topics, lists of the necessary materials and reagents, step-by-step, readily reproducible protocols, and tips on troubleshooting and avoiding known pitfalls. Concise and easy-to-use , Cell-Penetrating Peptides: Methods and Protocols, Second Edition hopes to raise relevant questions for further development.