This book provides a comprehensive introduction on the rainfall characteristics in a tropical area, Indonesia, on a time scale monthly to interannual. Unlike the monsoonal South Asia and East Asia, the Southeast Asian monsoon, especially over Indonesia is still not well understood. Chapters of this book stand for basic pillars in the rainfall characteristics in Indonesia; from the representation of rainfall from observation, representation of rainfall in the global model or reanalyses, representation of rainfall in the regional climate model, the introduction of the ocean climate in Indonesia related to the rainfall and the coupled ocean atmosphere aspects of the Indonesian rainfall. This book covers basic annual patterns and their regionalizations as well as ocean atmosphere mechanisms that drive them and how those annual patterns interplay to regional phenomena such as ENSO. The objective of this book is to describe how well the performance of multi level climate models over the tropics, especially in the representation of Indonesian rainfall. The reader of this book shall be the climatologist, atmospheric science, oceanographer and hydrologist who are interested in the climate and air sea interactions of the tropics.