The endeavour to prove the existence of God through reason and rational argumentation formed a key element of medieval Islamic theological and philosophical discourses - this is an assumption frequently articulated in the secondary academic literature devoted to the subject. But is this really the case? The discourse these theologians and philosophers are said to have participated in is commonly compared to the discourse on arguments for the existence of God formulated in western philosophy: both traditions, as it were, it is argued are concerned with proving that God exists. This thesis, however, argues that proofs for God's existence are actually absent from the theological and philosophical works of the classical Islamic era (3rd/9th-7th/13th centuries). This is not to say that the arguments we encounter there are flawed or unconvincing arguments and do not succeed in proving what they set out to establish: that is, God's existence. Reviewing the constellation of arguments and discussion germane to this subject, this thesis argues that medieval Islamic theologians and philosophers did not seek to prove that God exists, but that there existed an entirely different purpose which informed their endeavours. Various indications can be found that suggest the need for a reappraisal of the discussions in question, and this thesis shall identify them. Since we seek not only to identify what it is the participants of this discourse sought to prove, but also to examine its development with regards to the use of arguments, concepts and terminology - the former would, obviously, not be possible without the latter - we shall approach our sources in a chronological order with eight chapters being dedicated to a number of the most important classical Islamic theologians and philosophers.