Since the 1970’s scientists have aimed to understand the mechanisms that link cell cycle progression to cell growth. This work explores how cell growth and cell size are regulated at cell cycle entry. To do so, we revisited the canonical model for cell cycle entry, and with the goal of filling key gaps in the field. We used new approaches that allowed us to conditionally manipulate protein levels at specific times; thus allowing us to obtain a better understanding of their roles at specific cell cycle stages. This thesis is divided into three main chapters. Chapter 1 is an overview of the field and how the canonical model originated. Chapter 2 summarizes key findings that suggest that the canonical model needs to be revised. In Chapter three, I describe unpublished experiments that support findings in Chapter two.