Regulation of cell motility Cell migration is critical for embryonic development and tissue repair and often goes awry during disease processes such as cancer. Despite this clinical significance, most of our knowledge surrounding how cells move stems from in vitro assays of limited physiological relevance. To begin to extrapolate some of our in vitro understanding of cell motility to an in vivo scenario, we are exploiting the embryonic developmental dispersal of Drosophila (fruit fly) macrophages (hemocytes). Much like human macrophages, these cells are crucial for innate immunity and are necessary for responses to infection and tissue damage. We have developed a number of microscopy techniques that allow us to image these cells migrating in vivo, during both wound responses and embryogenesis, at a spatial and temporal resolution approaching what can be achieved from cells in culture. This attribute, along with the genetic tractability of flies, enables us to examine the genes and cytoskeletal responses driving migratory processes within a living animal. This system has allowed us to elucidate the intracellular cytoskeletal dynamics controlling how cells move and coordinate the migratory process, along with the extracellular cues driving migration during development and tissue repair. We are also extrapolating this knowledge to other cell types and model systems with the goal of highlighting fundamental mechanisms controlling cell motility.