The question of the nature and scope of Italian humanism, and particularly of humanist philosophy, has been an ongoing source of debate among historians. In this dissertation I explore the nature of humanist philosophy by complementing the traditional study of the "history of ideas" with that of the "history of practices." Concentrating on Petrarch's voluminous corpus of writing, I argue that Petrarch develops in his works a new ethical program, a new philosophy of self, at the centre of which is the assertion that "self" is above all a state of mind from which we are exiled and which we need to cultivate through constant practice, and particularly through the literary practice of writing (which is always intertwined with that of reading). In order to examine Petrarch's philosophy, therefore, this thesis focuses especially on his uses of writing as a spiritual exercise in his works, and the ways in which these uses both absorb and transform ancient and medieval traditions of writing. In Petrarch's vernacular poetry, I argue, writing serves mainly as a personal ritual and a meditative exercise that allows the poet to overcome his experience of fragmentation and exile by reviving and intensifying his desire. In the Latin works, in contrast, writing mostly serves as a vehicle for the cultivation of virtue and the eradication of desire, which is presented as the very source of the experience of exile. Nonetheless, the uses of writing in the Latin works, modeled mostly upon the example of Seneca, are in themselves persistently undermined by the "Ovidian" realization that writing is always tainted by desire, and is hence in itself part of the problem no less than the solution. This realization, in turn, also leads to the "Augustinian" backlash in Petrarch's works against secular writing in general. As a result, while this thesis argues that Petrarch's humanism is defined above all by his emphasis on care, his attempt to establish humanism as a form of secular spirituality, it also inevitably brings to the fore the tensions and contradictions that plagued his project from its onset.