We will touch briefly on the foundations of Stems and Branches, then explore the world of Five, the ten Heavenly Stems (tiangan 天干) in more detail. What are they? How do they affect humans? When and how can we use these ideas in our practice? These questions and more will be discussed, although as this subject matter is vast, we can merely hope to scratch the surface! We will look at the relationship between Stems and space, and their role as the foundation of wuxing 五行 Five Phases. This will extend our understanding of the interactions between zangfu 臟腑 organs and open the door to a discussion of practical applications.