To prepare the theoretical foundation for the rest of this book, in this chapter, we will study based on the basic attributes of the yoyo model the structure of meridian fields that helps to hold the dynamic spin field of the yoyo model together and some of the elementary properties of this model. Then, for the completeness of this book, we will glance through the theoretical and empirical justifications on why each and every system can be seen as a rotational yoyo.