Diatoms live in a diverse range of aquatic habitats with species being either free floating (planktonic) or attached to underwater structures (benthic). Ancestrally, diatoms are thought to have been planktonic with nonmotile vegetative cells and motile, flagellated cells for sexual reproduction. The single loss of motile, flagellated gametes in the common ancestor of pennate diatoms was a significant evolutionary step that was associated with the development of active motility in vegetative cells, which enabled outcrossing and their migration into previously inaccessible habitats (Nakov et al., Accelerated diversification is related to life history and locomotion in a hyperdiverse lineage of microbial eukaryotes (Diatoms, Bacillariophyta). New Phytol 219:462--473, 2018). The motility of benthic diatoms allows cells to actively maintain their position in the photic zone, avoid desiccation (e.g., during tidal fluctuations), identify optimal nutrient conditions, and perform sexual mating. The ability of motile diatoms to actively respond to changing environmental conditions provides a substantial selective advantage. Therefore, the evolution of migration ability is believed to be one of the reasons for diatom success and high rates of diversification in benthic habitats. In this chapter, we will review the current literature on the mechanism of cell motility, the extracellular signals that mediate cell motility, and the molecular composition of diatom adhesives.