My paper examines the content and reception of a disputed treatise on jihad attributed to the Syrian Ḥanbalī scholar Ibn Taymiyya (d. 1328), a text that has drawn considerable attention from both Wahhabi and modernist Muslim thinkers alike appealing to the latter’s authority. The work, called Qāʿida fī qitāl al-kuffār (“A Principle Concerning Fighting the Unbelievers”), is essentially a fatwa arguing that unbelief alone does not suffice to justify fighting the unbelievers but rather that they must pose a belligerent threat to warrant engagement. Beginning in the early twentieth century, the leading Wahhabi scholars of Najd dismissed the work as a forgery, leading to its effective prohibition in Saudi Arabia and subsequent exclusion from the Saudi-sponsored collection of Ibn Taymiyya’s writings, Majmūʿ al-fatāwā. Nonetheless, a network of Wahhabi or pro-Wahhabi scholars, from Egypt to the Ḥijāz to Qāṣīm, found nothing objectionable about Qāʿida fī qitāl al-kuffār and continued copying it into the 1940s, when if was finally published in Cairo under the auspices of the prominent Egyptian Salafī scholar Muḥammad Hāmid al-Fiqī. (I have gathered all extant manuscript and published copies of the text.) Most recently, modernists like Yūsuf al-Qaraḍāwī have seized on the work as evidence of the modernist interpretation of jihad as exclusively defensive warfare. To give some sense of the meaning of this controversy, my paper takes the following approach. First, I examine carefully what exactly the author of the treatise in question is arguing; namely, is he saying, (i) “Do not invade infidel countries unless they attack you,” or is he saying, (ii) “Invade infidel countries, but do not fight unbelievers unless they fight you first”? Second, having concluded that the author’s argument is likely the second of these, I evaluate the work’s attribution to Ibn Taymiyya in light of this argument’s correspondence to Ibn Taymiyya’s statements elsewhere, as well as those of his pupil Ibn Qayyim al-Jawziyya (d. 1350). I furthermore examine the work’s premodern scholarly reception, particularly in nineteenth- and twentieth-century Yemen. Third, having determined that the work is almost certainly genuine, I turn to its Wahhabi refutations, penned by no less than two grand muftis of the Saudi kingdom, and the contending works favoring the attribution. The discussion here points up variant readings of Ibn Taymiyya between Wahhabi and modernist circles, as well as variant readings between Wahhabis themselves, too often seen as forming a homogeneous religious community.