Silicon is the second most abundant element in the Earth's crust, making up about onequarter of the crust by mass. In the modern surface waters of recent oceans, silicon is undersaturated, but it is estimated that its concentration was much higher before the rise of the diatoms during the Jurassic–Cretaceous periods. Since silicon is everywhere, it is not surpris ing that, over time, a large number of marine and terrestrial organisms have acquired or developed the ability to use or to transform silicon. It is generally known that many organisms accumulate and/or use silicon to construct inter nal or external skeletons. One such organism is diatoms, a class of photosynthetic microalgae capable of creating beautiful threedimensional silica structures, called frustules. The importance of silicon has also been demonstrated by numerous studies in plants showing that silicon improves the resistance to diseases and mitigates other biotic or abiotic stresses. In this article, I highlight selected studies that aimed to understand the meta bolism of silicon, with a particular emphasis on the diatoms.