This book aims to help readers learn about formal specification using the Z language. The author argues that formal specification offers benefits to the developers of computer systems and that it will make a contribution towards improving their quality. The book is primarily aimed at those who are not as familiar with mathematics as the mathematician and in this respect certain aspects of the explanations have been kept more informal and given less emphasis than others. The chapters of this book contain explanations of the mathematics of Z, interleaved with the development of an example specification. The chapters covering mathematics finish with a summary of the notion introduced in the chapter and a set of exercises. Sample solutions to selected exercises are included in the appendix.