The main purpose of this book is to introduce the reader to the subject of solar activity and the connection with Earth's climate. It commences with a brief review of the historical progress on the understanding of the solar-terrestrial connection and moves on to an objective scrutiny of the various hypothesis. The text focuses on how knowledge about the solar cycle and Earth's climate is obtained. It includes discussion of observations, methods and the physics involved, with the necessary statistics and analysis also provided, including an examination of empirical relations between sunspots and the Earth's climate. The author reviews plausible physical mechanisms involved in any links between the solar cycle and the Earth's climate, emphasizing the use of established scientific methods for testing hypothesized relationships.