Stephen Hawking's worldwide bestseller, A Brief History of Time, has been a landmark volume in scientific writing. Its author's engaging voice is one reason, and the compelling subjects he addresses is another: the nature of space and time, the role of God in creation, the history and future of the universe. But it is also true that in the years since its publication, readers have repeatedly told Professor Hawking of their great difficulty in understanding some of the book's most important concepts. This is the origin of and the reason for A Briefer History of Time: its author's wish to make its content more accessible to readers -- as well as to bring it up-to-date with the latest scientific observations and findings.