This accessible volume presents an overview of the field with an emphasis on the new superconducting materials. After an elementary introduction to superconductivity, the authors highlight those properties most essential to understanding electromagnetic absorption of the superconducting state. They then outline both basic theories and salient experimental results, emphasizing qualitative aspects and experimental measurements. Readers will gain not only a basic understanding of the subject but also an appreciation of the wealth of information provided by electromagnetic absorption measurements, as well as insights into the mechanisms of absorption.