Diego de Avendaño (1594-1688) was born in Segovia. During his studies in Seville, he met Juan de Solórzano Pereira and accompanied him to the New World. Avendaño continued his studies in Lima at the Colegio San Martín of the Jesuits, joined the order himself and taught and led the Jesuitic colleges and universities in Cuzco, Charcas and Lima in the following decades. After, as he himself said, «almost fifty years in Peru» he published his main work, the six-volume Thesaurus Indicus, in which he discusses a wealth of questions of secular administration and spiritual practice. All six volumes will appear successively in the Digital Collection of Sources of the project «The School of Salamanca». A start has now been made with the first volume devoted to the questions of the secular regiment of Peru in the 16th and early 17th centuries.