Accounting for almost one-fifth of the primary production on Earth, the unicellular eukaryotic group of diatoms plays a key ecological and biogeochemical role in our contemporary oceans. Furthermore, as producers of various lipids and pigments, and characterized by their finely ornamented silica cell wall, diatoms hold great promise for different industrial fields, including biofuel production, nanotechnology, and pharmaceutics. However, in spite of their major ecological importance and their high commercial value, little is known about the mechanisms that control the diatom life and cell cycle. To date, both microscopic and genomic analyses have revealed that diatoms exhibit specific and unique mechanisms of cell division compared with those found in the classical model organisms. Here, we review the structural peculiarities of diatom cell proliferation, highlight the regulation of their major cell cycle checkpoints by environmental factors, and discuss recent progress in molecular cell division research.