Gravitational waves were predicted by Einstein over 75 years ago, but have not yet been seen. This book is about the technology of the new generation of interferometric gravitational wave detectors now being built, such as the LIGO (Laser Interferometric Gravitational-Wave Observatory) project in the US. The book aims to make plain how these detectors function, and why it is reasonable to think that gravitational waves may be successfully detected in the next decade.After an introduction to the physical and astronomical aspects of gravitational waves, the book concentrates on explaining the basic principles behind the detectors and discusses the strategies for utilising them. All the required background in astronomy, optics and experimental physics techniques is developed within the text, and anyone with an undergraduate knowledge of physics will be able to follow the arguments presented. The book will be of use not just to physicists and astronomers who wish to acquaint themselves with the subject, but will also prove useful for courses in experimental physics at the advanced undergraduate and graduate levels.