Book excerpt: Metrology is the scientific study of measurement. It establishes a common understanding of units, crucial in linking human activities. The knowledge of this subject is essential for all persons irrespective of the branch of engineering. For engineering purposes, the study is restricted to the measurement of lengths, angles and the quantities which are expressed in linear and angular terms. This book gives information about various instruments used for linear as well as angular measurements and corresponding errors. This book also includes concepts of quality, quality control, different tools and techniques for quality control, total quality management and various latest methods of quality control. Our hope is that this book, through its careful explanations of concepts, examples and figures bridges the gap between knowledge and proper application of that knowledge.