The ability to change shape and move is critical for the function of cell types ranging from single celled amoeba to immune cells and neurons. Similarly, the ability of organelles to change shape and move plays an essential role in intracellular transport. We are studying the engine that controls cell and organelle shape and movement, the actin cytoskeleton, using a combination of cell biological, biochemical and genetic methods. We are working to determine how actin filament assembly is initiated, how it is regulated, and how it functions during processes such as whole cell migration and membrane trafficking. Moreover, we are working to understand how diverse bacterial and viral pathogens target the actin cytoskeleton of host cells to promote pathogen internalization, replication and spread during infection.