Behavior that is oriented with respect to some goal is said to be intentional. In order for an intention to be fulfilled by a system, whether an individual or a social unit, it must serve as a global constraint on the local actions of that system (e.g., the location of a target constrains how the act of throwing is assembled; the desired facial profile constrains orthodontic treatment planning). Intentional behavior requires prospective, anticipatory control. How can the current dynamics of a system, the forces it must produce, the energy it must use, the number of participants engaged in an act, all be constrained by a goal that lies in the future, perhaps years away? What kinds of systems can be considered intentional? Experiments assess the consequences for behavior of manipulating intentions (e.g., navigate a wheel chair through clutter carefully or quickly)