This book offers a systematic approach to the study of those properties of Banach space complexes that are stable under certain perturbations. The stability of the index under small or compact perturbations is presented within the context of (semi-)Fredholm complexes. Various invariants and other properties are also considered. This raises certain problems requiring further study of more general Fredholm-type objects. Some of the results are new. Applications in several variables spectral theory and in other related fields are also given. Audience: This largely self-contained book...