INTRODUCTION CHAPTER l. CATEGORICAL ASPECT OF EQUIVARIANT HOMOTOPY: * Homotopy Kan extension and its applications; * Localization in simplicially enriched categories; * Fibre-wise localization and topological applications; CHAPTER 2. EQUIVARIANT HOMOLOGY THEORY: * Preliminaries; * Cohomology for J-spaces; * Applications; CHAPTER 3. RATIONALIZATION OF DISCONNECTED G-NILPOTENT SIMPLICIAL SETS: * Injective modules over a small category; * Object-wise tensor product of functors to modules; * Algebras over a category; * Cofibrant minimal models and formality; * Injective minimal models; * Applications to rational homotopy theory; CHAPTER 4. MOORE G-SPACES: * Background; * Comultiplications; * An example; REFERENCES INDEX