Chaotic phenomena flourish in nature. They often originate in systems whose components are governed by simple laws, but whose overall behaviour is very complex. This text aims to give an elementary introduction to the theory of chaotic systems and to demonstrate how chaos and coherence are interwoven into some of the simplest models exhibiting deterministic chaos. This is part of a theory more formally known as dynamical systems theory. Extensive use has been made of Lyapunov models, throughout the text, as a tool that can make the exploration of a particular model less time-consuming. There is also discussion of time series analysis, including analytical methods which have not become standard. Researchers making models intended to describe a time series are provided with a guide to scaling dimensions which gives the minimum of variables needed in the model.