Opticks is Newton's most popular book. It is a complex work, the fruit of forty years of thought and investigation. Newton devoted various periods of experimentation to this final expression of his life's work and drew on the results of successive interactions with other scientists and thinkers. This introduction to his book seeks to disentangle the different layers of his thought in the light of these influences while explaining the development of the final text. It faces the problem of the changes in Newton's ideas in the course of the book's long preparation, touching on such deep questions of natural philosophy as atomism, forces, and the aether. The author also looks in detail at the way Newton has been interpreted both at home and abroad. This book, with its readable style and nonmathematical approach, should serve as an introduction to this area of Newton's science seen in the context of eighteenth century thought in Europe.