In ordinary life reliability is an ephemeral but desirable property of a machine or service that is generally judged in a very subjective manner. For an engineer reliability has large cost and sometimes safety implications; it is therefore very important to be able to quantify it. This book is an introduction to reliability analysis aimed at engineers (not statisticians). As such it begins by assuming no prior statistical knowledge. It teaches by examples taken from engineering problems. Exercises are built around real machines and events and the solutions given illuminate the subject. Being able to quantify reliability allows engineers to quantify its financial implications in terms of maintenance policies, running costs, and spares stockholding. In safety critical situations (transport or military equipment) the implications are wider. In any complex project it is extremely important to be able to make reliability predictions.