Do we have control over our actions? If we do, what sort of control and to what extent? Free will is the power to act without the constraint of necessity or fate. It is the ability to act at one's own discretion. For centuries, people have wondered how freedom is possible in a world ruled by physical determinism. Reflections on free will have been confined to philosophy until half a century ago, when the topic started also to be seriously investigated by neuroscientists. Today, there are several irreconcilable positions about the existence of human free will.