There are many books which set out the more commonly used statistical methods in a form suitable for applications. There are also widely available computer packages for implementing these techniques in a relatively painless way. We have in the present book concentrated not so much on the techniques themselves but rather on the general issues involved in their fruitful application. The book is in two parts, the first dealing with general ideas and principles and the second with a range of examples, all, however, involving fairly small sets of data and fairly standard techniques. Readers who have experience of the application of statistical methods may want to concentrate on the first part, using the second part, and better still their own experience, to illuminate and criticize the general ideas. If the book is used by students with little or no experience of applications, a selection of examples from the second part of the book should be studied first, any general principles being introduced at a later stage when at least some background for their understanding is available.