To better understand the relationship between Deleuze and Kierkegaard, it will be helpful to first situate these two philosophers with respect to a particular history of post-Kantian philosophy from which they both derive several of their basic concerns and preoccupations. In looking at this tradition of post-Kantian philosophy, we will come to better understand two important vectors of both Deleuze's and Kierkegaard's thought. On the one hand, we will gain some understanding of the broader philosophical orientations of these two philosophers, especially around some common scepticisms regarding the adequacy of rational thought to grasp the specificity and materiality of existence. On the other hand, we will learn something about a specific philosophical narrative that serves to link ethical and psychological (in the sense of ‘rational psychology’ or ‘the study of the soul’) problematics in Kantian and post-Kantian philosophy and see how this association carries over into the close connection between ethical and psychological-existential issues in Kierkegaard's and Deleuze's work. By looking at the post-Kantian tradition, we will see that questions about ethical obligation and the possibility of moral judgement carry an important weight for questions about the nature of the self and indeed about the possibility of stable personal identity more generally. Here I simply want to situate these two philosophers at the end of a philosophical trajectory that leads from the Kantian critique of the possibility of self-knowledge, through a post-Kantian attempt to resuscitate the validity of the noumenal self, and finally towards a Romantic rejection of the possibility of apodictic self-knowledge. This sequence will show how questions about personal identity as they are inherited by both Kierkegaard and Deleuze are grounded in problematics associated with moral judgement and rationality, and also justify my premise that for both Kierkegaard and Deleuze the question of self-knowledge and the nature of the self remain central inheritances from the Kantian and post-Kantian tradition. I will subsequently investigate some more specific points of contact, around the concept of repetition in Chapter 2, and the concept of non-prescriptive ethics in Chapter 3. In the fourth chapter I will return to these reflections on the nature of the self in order to sketch how each of these thinkers elaborates their own reformulation of the nature of personal identity, especially in line with some of the more Romantic ‘aesthetic’ elements inherited from the immediate post-Kantian period.