Nature presents examples of active sensing which are unique, sophisticated and incredibly fascinating. There are animals that sense the environment actively, for example through echolocation, which have evolved their capabilities over millions of years and that, as a result of evolution, have developed unique in-built sensing mechanisms that are often the envy of synthetic systems. This book presents some of the recent work that has been carried out to investigate how sophisticated sensing techniques used in nature can be applied to radar and sonar systems to improve their performance.