Semi-arid regions are ecological security barriers that prevent arid regions from expanding and turning into deserts. The expansion of arid regions and desertification seriously threaten ecological security, and human society cannot achieve sustainable development in an insecure ecological environment. As the transitional zone between arid and humid regions, semi-arid regions lay the foundation of ecological safety for the development of human society.This book provides an overview of processes and mechanisms that characterize semi-arid climate change both regionally and globally. It explains systematically theoretical concepts , including land-atmosphere interactions, ocean-atmosphere interactions, and factors that contribute to climate change, including the impact of human activities. A summary of recent progress in the research in the field and the future of semi-arid regions are also discussed.This book is a specialized monograph and textbook for graduate students of Earth sciences. It is also suitable for undergraduate or graduate students in related majors such as those engaged in atmospheric science, climate change studies, and Earth sciences.