The intricate morphology of diatom cell walls has fascinated scientists since the invention of the light microscope more than 300 years ago. However, it was not recognized until 1844 that the diatom cell wall, termed frustule (from Latin frustulum = piece, chunk), is actually mainly composed of glass (amorphous SiO2 or silica). As more and more details of frustule structures from numerous species were revealed through improvements in light microscopy and the development of electron microscopy, it became increasingly mysterious as to how such amazingly complex inorganic architectures are produced by individual cells. The species-specificity of the frustule structure indicates that the blueprint for its morphogenesis is encoded in adiatom’s genome. Unveiling the machinery that executes this morphogenesis program is still ongoing (see also Chap. “Biomolecules Involved in Frustule Biogenesis and Function”). Here, we explain the general architectures of frustules and describe the main cellular events and key steps in their morphogenesis.