This dissertation focuses on the study of a fiscal institution – the almoxarifados – and its agents – the almoxarifes –, during the reign of D. Afonso IV (1325-1357). In the first part are analyzed the origins (from D. Sancho I to D. Sancho II) and the development of this institution (D. Afonso III and D. Dinis) interpreting, not only the organization of the tax bureaucracy, in the context of the increasing administrative complexity, but also the transition from the functions flexibility to a clear definition of the responsibilities of these officers. In the second part, already in the reign of D. Afonso IV, it is analyzed the organic and functional affirmation of the almoxarifados, based on the chancery documentation and on the legislation to regulate this institution. So, they are identified the organic units that composed the almoxarifados network, questioning their various typologies. In the same way, they are identified the almoxarifes who were responsible for each unit, defining their functions and responsibilities and analyzing their representation in the Cortes of D. Afonso IV.