The remarkable contributions in the 23 articles by the 49 authors from a dozen different countries, presented in The Diatom World, offer new data on diatoms. This volume celebrates the diatoms’ diversity, emerging areas of research on them, and their fascinating ecology. The chapters relate to age-old questions and topics, such as the classification of diatoms and the habitats they occupy, as well as address new areas of research and interest, such as diatom viruses, symbioses, nanotechnology, and toxicity. In this combination of persistent questions and new horizons, it is clear that the diatoms remain as alluring and intriguing today as they were when Von Leeuwenhoek first spied them over 300 years ago. We suspect interest in this group will grow in the years to come as many new fields emerge around their biology, geological record, genomics, incredible morphologies, and ecological breadth.