A statement or action can be said to be manipulative if it does not sufficiently engage or appeal to people’s capacity for reflective and deliberative choice. One problem with manipulation, thus understood, is that it fails to respect people’s autonomy and is an affront to their dignity. Another problem is that if they are products of manipulation, people’s choices might fail to promote their own welfare, and might instead promote the welfare of the manipulator. To that extent, the central objection to manipulation is rooted in a version of Mill’s Harm Principle: People know what is in their best interests and should have a (manipulation-free) opportunity to make that decision. On welfarist grounds, the norm against manipulation can be seen as a kind of heuristic, one that generally works well, but that can also lead to serious errors, at least when the manipulator is both informed and genuinely interested in the welfare of the chooser. For the legal system, a pervasive puzzle is why manipulation is rarely policed. The simplest answer is that manipulation has so many shades, and in a social order that values free markets and is committed to freedom of expression, it is exceptionally difficult to regulate manipulation as such. But as the manipulator’s motives become more self-interested or venal, and as efforts to bypass people’s deliberative capacities becomes more successful, the ethical objections to manipulation become very forceful, and the argument for a legal response is fortified. The analysis of manipulation bears on emerging first amendment issues raised by compelled speech, especially in the context of graphic health warnings. Importantly, it can also help orient the regulation of financial products, where manipulation of consumer choices is an evident but rarely explicit concern.