This lecture covers the regulation of the mammalian cell cycle, focusing on the events around the R point transition. Topics include the role of p27 and p21 in inhibiting CDK activity, the formation of CDK4/6-Cyclin D complexes, and the phosphorylation of RB protein. The lecture also discusses the activation of CDK2-CycE, the ubiquitylation and degradation of p27, and the phosphorylation levels of RB throughout the cell cycle.