The general principles of polar rearrangements are brought together in this text, which deals with all the major rearrangements involving electron-deficient atoms or charged intermediates. Reactions involving migration to electron-deficient carbon, nitrogen, oxygen and sulphur, and sigmatropic rearrangements involving polar species, are thus treated in a coherent and consistent manner. Clear discussions of the reaction mechanisms are followed by examples of synthetic applications providing a concise yet comprehensive account of the nature of and importance of these processes.