Functional electrical stimulation is the most important application in the field of clinical treatment with currents or magnetism. This technique artificially generates neural activity in order to overcome lost functions of the paralized, incontinent or sensory handicapped patient. Electricity and magnetism is also used in many cases, e.g., to stimulate bone growth or wound healing. Nevertheless, the basic mechanism of the artificial excitation of nerve and muscle fibers has become known only in the last few years. Although many textbooks are concerned with the natural excitation process there is a lack of information on the influence of an applied electrical or magnetic field. This book, written for students and biomedical engineers, should close the gap and, furthermore, it should stimulate the design of new instrumentation using optimal strategies.