Introduction

Different aspects of the evolution of galaxies include dynamical, involving diffuse material (‘gas’, which will be understood to include dust), stars and dark matter; thermal (mainly affecting the gas); photometric + spectrophotometric (involving stars and gas); and so-called galactic chemical evolution (GCE) which is not really about chemistry (an important topic in its own right) but concerns the origin and distribution of nuclear species (loosely referred to as elements) in stars and gas. True insights into the origin and evolution of galaxies need studies of all these different aspects and their inter-relations, but there are several results of GCE that can be at least partially understood using only the very broadest ideas about other poorly understood aspects (e.g. the physics of galaxy and star formation) and this makes GCE a topic that is worth studying in its own right. At the same time, there are still many uncertainties, both in the underlying theory of stellar evolution, nucleosynthesis and mass loss and in the galactic context in which these basic element-forming processes take place. These limit the extent to which safe deductions can be made and motivate one to use the simplest possible models. The present chapter describes some basic principles, while the following one will discuss some specific models and related observational results.