This book provides the reader with an insight into the dominant factors determining the specific transmembrane transfer processes in proteins. The authors discuss high-field EPR in conjunction with site-specific mutation strategies and employ advanced quantum chemical computation methods for data interpretation in order to reveal fascinating protein structures and dynamics. Both theory and practise are covered, including state-of-the-art high-field EPR research both in terms of instrumentation development and application to paradigmatic biological systems and future perspectives.