The aims and intended audience of this second edition remain unchanged from the first edition. The aim is to provide the underpinning knowledge of physics and instrumentation needed in order to practise ultrasound in a clinical setting. The book is primarily aimed at sonographers and clinical users in general, and will also serve as a first textbook for physicists and engineers. The text concentrates on explanations of principles which underpin the clinical use of ultrasound systems. The book contains relatively few equations and even fewer derivations. In the last 7 years a number of techniques which existed in embryo form in 2002 have become available on commercial ultrasound systems, and are used in a sufficient number of hospitals to justify inclusion in this book. There are additional chapters dedicated to 3D ultrasound, contrast agents and elastography. The other chapters have been updated to include developments in technology, quality assurance and safety. We hope that this second edition of ‘Diagnostic Ultrasound Physics and Equipment’ will meet the needs of sonographers, physicists and engineers in their training and practice.