Magister Artium - MA / Our secular age is a period of scepticism and ubiquitous doubt. The epistemology of a paradigmatic figure like Abū Ḥāmid al-Ghazālī (1058-1111) is central to Islamic intellectual thought, but also speaks to our modern world. In this research dissertation we embark on a critical study of doubt (shakk) and certainty (yaqīn) in Ghazālī’s epistemology. We ask, what is the nature and function of doubt, and how do we best acquire truth and certainty according to Ghazālī? In our evaluation of scepticism in Ghazālī’s epistemology, we analyse the notion of existential doubt and his methodological doubt. In the latter, we look at his scepticism of the methods of knowing as a means to establish the foundations of knowledge. Also, we look at his scepticism as an instrument to cast doubt upon heterodox doctrines and show the limitations of philosophical logic. In this study we assess Ghazālī’s attitude to philosophical demonstration and Sufism as a means to certainty. In early scholarship surrounding Ghazālī, it was assumed that he was a vehement adversary to philosophy. On the other hand, in much of contemporary scholarship, Ghazālī has been understood to give preference to philosophy as the ultimate means to certainty, undermining the place of Sufism. In this study we evaluate these claims; we argue that he was not antagonistic to philosophy and regarded it as a legitimate approach to certainty, but recognised Sufism as a superior approach. Much of previous scholarship has either focused on Ghazālī as a Sufi or a philosopher; we attempt to embark on a parallel approach in which we acknowledge each discipline in its right place within Ghazālī’s epistemology. Thus, in analysing Ghazālī’s approach to acquiring certainty, we evaluate his foundationalism, his attitude to authoritative instruction (taʿlim), and the place of philosophical demonstration and Sufism.