What we count as manipulation, and what means we regard as possible to achieve it, depends partly on our view of how agency and cognition work in the target of manipulation. Mainstream thinking about the mechanisms of manipulation tend to assume cognitive internalism, where cognition is performed by brains that relate to the world through sense and motor control. Here I review the two most common cognitive internalist approaches to thinking about manipulation, in expected utility theory and prospect theory. Then I focus on manipulation of behaviour taking as a starting point the view that human cognition is extensively scaffolded. Cognition is scaffolded when it relies in significant ways on structure and resources external to the skull and skin. When cognition itself extends into the outside world, it can be manipulated by means of external interventions. This isn’t merely a speculative possibility. There are real examples of manipulating scaffolded human cognition.