La tesi introduce, commenta, annota e contestualizza le lettere inedite del critico e scrittore Giovanni Testori al suo maestro Roberto Longhi. Vengono poi approfonditi gli elementi di novita' che emergono dalle lettere: sulla Milano artistica degli anni '50, sulla produzione letteraria di Testori e sulla sua idea di critica d'arte. Conclude la tesi una fitta antologia di interventi di Testori dedicati al maestro. / This thesis is a study and a critical analysis of the unpublished correspondence between the art critic and writer Giovanni Testori and his master Roberto Longhi considered within its historical and cultural context. In particular this study is focused on topics that have never been considered before, such as the artistic production typical of the city of Milano during the fifties in relation to Testori's literary work and his thought on the critic of art. The work ends with a wide appendix consisting in a collection of Testori's essays and articles on Longhi.