Engineered devices are often made of rigid components, but nature is full of flexibility. This is especially apparent in small-scale swimmers, which commonly use highly deformable bodies and appendages in interactive, coordinated ways. However, we know very little about how these flexible surfaces and structures coordinate to create the complex fluid flows necessary for locomotion and sensing—and how we might be able to develop bioinspired technology based on these remarkably successful creatures. Using new methods at the intersection of biology and engineering, we will investigate how flexible biological structures work together to create and control flow at the millimeter scale. Our results will help inform the design of a new generation of soft robotic sensors, devices, and micro-vehicles, and provide a deeper biological understanding of how animals use flexibility to survive and thrive.