Abstract: In recent philosophical and theoretical debates, the question of ethics has risen to new prominence and manifold suggestions have been made as to how to adopt ethics to the challenges of today's complex world. With the belief in idealist conceptions and universal principles gone, the backbone of traditional ethical thought---a morality of what is 'good' and 'right' on the basis of an idealist difference between 'what is' and 'what ought to be'---no longer holds as ethical measure. The problem of ethics can no longer rest on the presupposition of the ideality of the 'ought' and its corresponding logic of Being as the assertion of a reality that 'is'. This dissertation follows Gilles Deleuze's response to this problem as it has been laid out---albeit implicitly---in his philosophy. Instead of falling back into the idealist, i.e. transcendentalist, trap, Deleuze's radical affirmation of immanence---carved out here along his main influences Spinoza, Bergson, and Nietzsche---makes his philosophy fruitful for ethics because it overcomes the morality of 'good' and 'right' by a Nietzschean thought 'beyond good and evil'. In order to conceive of immanence in its radical potential, emphasis is put on the concept of 'becoming' that is at the heart of Deleuze's philosophy. Becoming not only structures his way of philosophizing, but always already affects this thought with ethico-political, i.e. practical implications. No longer looking for the solidity of Being whereupon to establish the moral prescriptions of 'what ought to be,' Deleuze's philosophy of becoming---and the ethical thought it carries---emphasizes life instead of law, singularity instead of universality, and multiplicity instead of a priori. As this dissertation suggests, the engagement with Deleuze's philosophy/ethics of becoming not only changes the parameters of how we think of ethics, but also of how we think of the relation of 'life and thought' itself, reformulating the relation between philosophy and ethics. Ethics is no longer simply one special field within the discipline of philosophy, but is internally connected to philosophy. The two thoughts inherently produce each other, and, as is argued, to approach ethics via a philosophy of becoming also means to approach philosophy as a practice of thought.