The luminosity of the sun governs the temperature of the planets. And the solar forcing, or driving, of climate, primarily due to changes insolar radiation, is an idea whose history has not been well documented in a book. Recent satellite measurements have shown that solar radiation varies as a function of wavelength - a concept that for the past two centuries scientists have claimed would be proved. Now, with all of the attention being given to global warming, this topic has again become timely. The book will review the physics of the concept of solar forcing in manageable terms, tracing its history from its beginnings in the early 1800s toits apparent success in the 1920s, to its near demise in the 1950s and its resurrection in recent years. Emphasis will be on solar variation as a driver for climate change, with only a brief discussion of other mechanisms - thus assuring the book a clear focus.