 Among Immanuel Kant’s (1724–1804) most influential contributions to philosophy is his development of the transcendental argument. In Kant’s conception, an argument of this kind begins with a compelling premise about our thought, experience, or knowledge, and then reasons to a conclusion that is a substantive and unobvious presupposition and necessary condition of this premise. The crucial steps in this reasoning are claims to the effect that a subconclusion or conclusion is a presupposition and necessary condition of a premise. Such a necessary condition might be a logically necessary condition, but often in Kant’s transcendental arguments the condition is necessary in the sense that it is the only possible explanation for the premise, whereupon the necessity might be weaker than logical. Typically, this reasoning is intended to be a priori in some sense, either strict (Smit 1999) or more relaxed (Philip Kitcher 1981, Pereboom 1990). The conclusion of the argument is often directed against skepticism of some sort. For example, Kant’s Transcendental Deduction targets Humean skepticism about the applicability of a priori metaphysical concepts, and his Refutation of Idealism takes aim at skepticism about external objects. These two transcendental arguments are found in the Critique of Pure Reason (1781, 1787), but such arguments are found throughout Kant’s writings, for example in the Groundwork of the Metaphysics of Morals (1785), in the Critique of Practical Reason (1788), in the Critique of the Power of Judgment (1790), and in the Opus Posthumum (1804; Förster 1989). This article focuses on the Transcendental Deduction, the Refutation of Idealism, and more recent transcendental arguments that are inspired by Kant’s work.