This work endeavors to realize an encompassing reading of the sonnets of Fernando Pessoa and his heteronyms, including the text-fixation and study of nearly three hundred poems written in Portuguese, English or French. This magnitude of corpus does not represent the entirety of the sonnets found during the research; although some unpublished poems are studied, more than fifty inedited English poems are put aside, with manuscripts still to be read and fixated. This work ventures to study Pessoa as one of the great sonnetists in Portuguese Literature, raising him to the stature of Camões, Bocage and Antero, when regarding his cultivation of the sonnet between tradition and aesthetic rupture. The reading of the poems is developed in three stages, corresponding to the three parts of the thesis: investigation, edition, study. The investigation, in which the methodology is detailed, discusses the philological and editorial challenges of dealing with the sonnets of Pessoa: where to find them, how to read and date them, which heteronyms to assign to them and which texts to include inside the definition of sonnet… The second part contains the sonnets themselves, with notes indicating our textual divergences from critical editions such as the ones by the Imprensa Nacional Casa da Moeda. The poems are accompanied by a synchronic apparatus of marginal icons, inviting the reading in diverse thematic sequences, beyond the chronological order. Lastly, part three weaves the conclusions of the investigation, as a series of thematic essays grouped in basic themes, language themes and philosophical themes, respectively approaching the elemental motifs, the poetic mechanisms and the paths to knowledge explored by Pessoa s sonnets.