Synopsis This book is a study of continuous changes in climatology. The use of the air mass concept in climatology, the principles of classifications and the evolution of the present day climates has been described briefly. In this book, the relevant geographical aspects of modern knowledge of physical, biological, agricultural and medical sciences contribute to the proper understanding of environment. Climate is explained in terms of a geographical factor, the variations of which influence the way of life of peoples in different regions. Without entering into the physics of meteorological processes, with which the student is expected to be already familiar, effect is as far as possible related to cause, and, since the book is intended primarily for geographers, prominence is given to the human aspect and the practical application.