Book excerpt: Supersymmetry is a symmetry which combines bosons and fermions in the same multiplet of a larger group which unites the transformations of this symmetry with that of spacetime. Thus every bosonic particle must have a fermionic partner and vice versa. Since this is not what is observed, this symmetry with inherent theoretical advantages must be badly broken. It is hoped that the envisaged collider experiments at CERN will permit a first experimental test, which is expected to revive the interest in supersymmetry considerably.This revised edition of the highly successful text of 20 years ago provides an introduction to supersymmetry, and thus begins with a substantial chapter on spacetime symmetries and spinors. Following this, graded algebras are introduced, and thereafter the supersymmetric extension of the spacetime Poincaré algebra and its representations. The Wess-Zumino model, superfields, supersymmetric Lagrangians, and supersymmetric gauge theories are treated in detail in subsequent chapters. Finally the breaking of supersymmetry is addressed meticulously. All calculations are presented in detail so that the reader can follow every step.