Max Born (1882-1970) was a physicist and mathematician who won the 1954 Nobel Prize in Physics for his research in the area of quantum mechanics. Originally published in 1943, this book presents a slightly expanded version of an address Born gave to the Durham Philosophical Society and the Pure Science Society, King's College, at Newcastle-upon-Tyne on 21st May 1943. The text provides an examination of the mutual relationship between theory and experiment in the development of physics. This book will be of value to anyone with an interest in the works of Born, physics and the history of science.