Acting for Reasons is about why we do what we do. It's also about how we arrive at an understanding of other people's actions. A traditional view in philosophy - 'Common-sense Psychology' - holds that mental states like beliefs and desires (states which provide a person's reasons for doing what they do) lie at the heart of intentional action and social cognition. According to this view, typically, what people do is a rational response to the reasons they have: I open the cookie jar because I'd like a cookie and believe there is one in there. As a corollary, understanding someone else's actions is held to depend on attributing them plausible mental states and reasoning: I think you opened the cookie jar because you wanted a cookie and believed there was one in there. This reasons-responsive understanding of action lies at the heart of crucial social notions like agency and responsibility. However, it has been thrown into doubt by experimental findings which apparently show that the common-sense appeal to reasons and reasoning is overly demanding and overly intellectualising, painting an idealised picture of decision-making which is rarely borne out by the evidence. If we get out of our armchairs and examine how people actually make decisions, the claim is, what we find is that people don't do what they do, typically, based on the reasons they have. Instead, people are swayed by biases and flaws in their reasoning systems, using cognitive heuristics (intuitive, gut-feel decision-making processes) which bypass the proper consultation of reasons. Furthermore, if we look at how animals, infants, and adults under time or other pressures understand the actions of others, what we find is that they appeal to simpler systems (e.g. looking only at environmental factors and overt behaviour), providing a route to action understanding that circumvents attribution of reasons and reasoning. In short, then, experimental findings show that common-sense psychology is wrong. This book is an attempt to reject that line of argument and defend the common-sense perspective, vindicating the core philosophical idea that, in the typical case, people do what they do for the reasons they have.