My laboratory investigates how cell growth triggers cell division to control cell size, a crucial factor in cellular function and organismal fitness. There are three primary mechanisms cells use to regulate size that are of interest to our lab: growth rate adjustments, geometric measurements of cell dimensions, and concentration-based biochemical signals. We have made the most progress on the later concentration-based mechanisms. We found that in budding yeast, cell division is triggered by the dilution of Whi5, a cell cycle inhibitor. As cells grow, Whi5 concentration decreases, leading to the activation of cell cycle genes and the initiation of cell division. This dilution model, tested across various organisms including human cells which dilute the functionally similar retinoblastoma protein, suggests that inhibitor dilution is a fundamental mechanism by which cells coordinate growth and division. Building on these findings, we are currently investigating the molecular mechanisms controlling cell cyclin inhibitor dilution in yeast and human cells. We are also working on better understanding the regulation of cell growth per se, and how this is influenced by cell size. Our research aims to expand the understanding of mechanisms and physiology of cell size and growth control, which are fundamental questions in cell and systems biology.