Cells across all kingdoms of life need to maintain tight control on their division process, which they use to replicate themselves. In particular, the decision of cells to initiate a round of division is a ubiquitous and essential process, whose dysregulation can dramatically affect cell viability in simple unicellular organisms, while contributing to carcinogenesis in organisms such as humans. The central goal of this proposal was to determine the key molecular mechanisms behind this decision process. To achieve this, we used a combination of cutting-edge experimental methods with data analysis and mathematical modeling to understand how and when individual budding yeast cells decide to divide. Our results have generated new fundamental knowledge on the regulation of the yeast cell division cycle which, thanks to the high degree of evolutionary conservation of cell division mechanisms among different organisms, may also be applicable to organisms such as humans.