Introduction

Abstract

A short presentation is given about how we conceive theoretically the solid state of matter, namely about its constituents and their interactions. The starting point is of course an oversimplified one, which afterwards one tries to improve and even redefine it. In the opposite sense, one tries later to simplify it in order to allow for theoretical calculations. In spite of all these problems, one gets predictions, that often may be successfully confronted with experiments. The different Chapters of this Compendium are however intended only to introduce the reader into the basic concepts of solid state theory, without the usual detours about specific materials and without comparison with experiments.