Introduction -- Chapter I The Landau Theory -- Chapter 2 Response of the System to External Excitations -- Chapter 3 General Properties of Green’s runctions -- Chapter 4 The Structure ofthe Elementary Excitations Spectrum -- chapter 5 Perturbation Methods -- Chapter 6 Interaction of Two Elementary Excitations -- Chapter 7 Generalization of Perturbation Methods to Superfluids -- Appendix A: Different Forms of the Correlation Function -- Appendix B: Second Quantization -- Appendix C: Some Properties of the Single-Particle Green’s Function -- Appendix D: Analytical Properties of K(k,wi) -- Appendix E: Wick’s Theorem -- Appendix F: Some Properties of Diagrams with Interaction Lines -- Notation -- References and Literature -- Index.