The Present book is primarily deals on reliability problems which is useful for the mathematics students as well as for the industry. In this book industrial problems regarding failure of machines and the maintenance polices are discussed. Different particular cases are given besides some basic concepts. Many books and journals have been consulted for the preparation of this text. We wish to thank the learned authors from whom valuable directions had been taken. We also express our sincere thank and appreciation to the Lambert Academic Publisher for publishing of this book.