Particular time-varying patternings of the limbs characterize activities such as running, juggling, and baseball batting. These movement patterns comprise many degrees of freedom at the neural and muscular level organized as a functional unit. What general principles are at work in their assembly, and what quantities capture their dynamical, macroscopic nature? Movement patterns change to meet task demands, for example, reflecting the type of terrain (steep, slippery) or the intent of the actor (staying in the middle of the path). Are these changes principled? Given that information guides the assembling of movement patterns, and the execution of acts, how is this information made available in dynamically relevant and task-specific ways, and how is it used? Experiments typically employ rhythmic behaviors to assess the consequences for coordination of varying aspects of the underlying dynamic.