Helobdella is a genus of freshwater leeches, several species of which have been used for developmental studies since the 1970s. Helobdella embryos have been used for cell-lineage tracing and dye-mediated photoablation, and they have also been very useful for studies in cellular neurobiology. In this article, we discuss the reasons that Helobdella is used for studying development and some of the questions that are addressed through the use of this organism.