The present chapter is devoted to the issue of periodization of Big History in terms of levels of complexity, peculiarities of its phases (main or transitional) as well as directions of these phases (main direction, lateral, or dead-end). We will try to give a rather detailed picture of the unfolding universal evolution, which consists of 10 phases rather than a short scheme: cosmic–biological (life, etc.)–social (history, mind, etc.). The notions of main and transitional phases of Big History are introduced; and the importance of its planetary and chemical phases is shown. Such a complete picture of Big History has never been created before. These ten phases in our scheme are divided into five main phases and five transitional phases. We are going to show that these ten phases in our Big History scheme are divided in five main and five transitional phases. This a) reduces the qualitative gap between the main phases of Big History; b) reveals the mechanisms of evolutionary development and of the transition to a higher level of complexity; c) shows the importance of the planetary and chemical phases. We have also introduced the idea of continuous lines of evolution, for example, chemical evolution.