The purpose of this chapter is twofold. First, it explores the different meanings of meditation and its varieties across Eastern and Western traditions, including the more recent therapeutic developments. Using a Meditation Tree image, specifically created for this volume, the chapter gives examples of practices from these traditions that rely on multiple techniques, such as concentration, recitation, breathing, singing, and visualization of physical or mental objects, among others. It highlights the richness of practices but equally of experiences and expected goals, which have led to debates and tensions among meditation experts and movements for over two thousand years. Second, the chapter summarizes the structure of this volume and the major achievements in the study of meditation, as well as current limitations and controversies.