The phenomenology of cell size control

Cells control their size through an intricate balance of cell growth, cell division, and cell death. Extensive work on unicellular model organisms revealed that cell-size-dependent cell cycle progression accounts for major aspects of cell size regulation and provided insights into the underlying molecular mechanisms. Nevertheless, elaborate live-cell imaging approaches still reveal new phenomenological observations that challenge our simplified models of size regulation and raise the question of what determines optimal cell size. Here, I aim to give a conceptual overview of the many processes contributing to cell size regulation and summarize recent developments in the field.