This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book describes a single equation choice model based on a single decision. It presents a range of issues that require some appreciation in a book on choice modelling, even though they are of more general relevance. Since the prime aim of discrete-choice modelling is to develop a forecasting capability, it is necessary to understand the issue of aggregating individual predictions to yield population predictions. The book explains the additional conceptual issues necessary in an introduction to applied discrete-choice modelling. Applied discrete-choice modelling can be viewed as the use of a variety of statistical techniques to quantify in a meaningful way a relationship between a discrete choice and a set of explanatory variables. The literature on discrete-choice modelling is spread widely across several disciplines, notably statistics, economics, psychology, engineering and sociology.