This book offers an overview of solar physics with a focus on solar activity, particularly the activity cycle. It is known that solar activity varies periodically, but there are also phases of intermittency, such as the Maunder minimum, during which solar activity is very low or high over several decades. The book provides a brief introduction to chaos theory and investigates solar activity in terms of its chaotic behavior. It also discusses how intermittent phases of solar activity have affected and can affect Earth's climate and long-term space weather, and reviews the underlying theories relating to the solar dynamo mechanism. Furthermore, each chapter includes references to scientific literature (review articles and papers) so that readers can delve deeper into the subjects covered. This richly illustrated book will appeal to a wide readership, and is also useful as a textbook for courses in solar physics and astrophysics.