famous equation, E = mc?. 1 hope that this will not scare off half ‘of my potential readers. ‘Apart from being unlucky enough to get ALS, or motor neuron disease, I have been fortunate in almost every other respect. The help and support I received from my wife, Jane, and my children, Robert, Lucy, and Timmy, have made it possible for me to lead a fairly normal life and to have a successful career. | was again fortunate in that 1 chose theoretical physics, because that is all in the mind. So my disability has not been a serious handicap. My scientific colleagues have without exception been most helpful. In the first “classical” phase of my career, my principal associates and collaborators were Roger Penrose, Robert Geroch, Brandon Carter, and George Ellis. I'm grateful to them for the help they gave me, and for the work we did together. This phase was summed up by the book, The Large Scale Structure of Spacetime, which Ellis and I wrote in 1973. 1 would not advise readers of this book to consult that work for further information: it is highly technical, and quite unreadable. I hope that since then I have learned how to write in a manner that is easier to understand. In the second “quantum” phase of my work, since 1974, my principal collaborators have been Gary Gibbons, Don Page, and Jim Hartle. | owe a lot to them, and to my research students, who hhave given me a great deal of help, in both the physical and theoretical senses of the word. Having to keep up with my students hhas been a great stimulation, and has, I hope, prevented me from ing stuck in a rut. Thave had a lot of help with this book from Brian Whitt, one ‘of my students. I caught pneumonia in 1985, after I had written the first draft. I had to have a tracheostomy operation which removed my ability to speak, and made it almost impossible for me to communicate. I thought I would be unable to finish it. However, Brian not only helped me revise it, he also got me using a ‘communications program called Living Center which was donated to me by Walt Woltosz, of Words Plus Inc, in Sunnyvale, California, With this I can both write books and papers, and speak to people using a speech synthesizer donated by Speech Plus also of Sunnyvale, California, The synthesizer and a small personal computer were