This volume of the Encyclopaedia offers a systematic introduction and a comprehensive survey of the theory of complex spaces. This is an important subject in the theory of several complex variables. Two of the authors, Grauert and Remmert, are internationally known outstanding experts who have developed substantial parts of the field. The authors have written for graduate students and researchers in complex analysis, algebraic geometry and differential geometry. The book will also be a valuable source of information for mathematical physicists.