The scientific study of weather patterns averaged over a period of time is called climatology or climate science. It focuses on recording and analyzing weather patterns of the Earth's atmosphere and understanding the conditions that cause them. It is a branch of the atmospheric sciences and a subfield of physical geography. Climatology also comprises aspects of oceanography and biogeochemistry. It is used for the analysis of observations and modeling the physical laws that determine the climate. It encompasses climate variability, mechanisms of climate change, and modern climate change. This book outlines the principles and applications of climatology in detail. It discusses the fundamentals as well as modern approaches of this field. As climatology is emerging at a rapid pace, the contents of this book will help the readers understand the modern concepts and applications of the subject.