This book provides leading edge research on a cell cycle, which is an ordered and highly controlled set of events that leads to cell growth and proliferation. Cell cycle progression is driven by changes in the substrate specificity and subcellular localisation of cyclin-dependent kinases (Cdks), which in turn are modulated by a collection of cyclins, Cdk-activating and Cdk-inhibiting kinases, and Cdk inhibitors (CDKIs). Regulation of the cell cycle is critical for the normal development of multicellular organisms and dysregulation of cell cycle could lead to cancer, a disease where normal cell growth and behaviour are lost. Cell cycle regulation is tightly controlled by both synthesis and degradation of short-lived proteins, such as cyclins and CDKIs, and degradation of these proteins is mainly mediated by the ubiquitin-dependent proteasome pathway.