The four homilies In principium Actorum originate in the Antiochene period of John Chrysostom's priesthood (386-397). Their liturgical frame is Easter time; the preacher is speaking especially to neophytes and aims at introducing his listeners to the book of the Acts of the Apostles, which they are not familiar with. In these texts the preacher explains the importance of titles (first homily), the word "Acts" (second homily), the word "Apostles" (third homily) and the reasons why this book is read just after Easter, and not after Pentecost (fourth homily). There used to be another homily about the author of the book of the Acts, which is now missing, between the first and the second homily. These homilies form an open "micro-series" which is strongly linked to other homilies (De mutatione nominum 1-4, In Genesim sermo 9, In illud: Si esurierit inimicus). The study of the direct manuscript tradition, the account of the indirect tradition (eclogae, anthologies, catena in Acta Apostolorum, Armenian tradition, encomium for the feast of saint Paul, testimony in Byzantine literature) as well as the analysis of the first editions make it possible to reconstruct the history of these four texts in preparation for their critical edition. It also confirms the coherence of the corpus, although the homilies have not always been transmitted together. The dissertation presents a new edition of the homilies In principium Actorum which is based on more reliable parts of the Greek tradition. A new French translation of the four homilies is also given. The commentary explores three important aspects. First, the preacher's method of introducing the Acts has consequences on the exegesis of the chosen biblical examples: the dissertation shows some of those consequences and questions the proximity to a continuous commentary and to texts from other authors (for instance Didymus the Blind). The importance of the mission in those homilies is then put forward: rooted in the feast of Easter, the call to mission creates a strong relationship between preacher, listeners and absentees. This last point leads to the apologetical aims of the texts: conversion is due to a shift in meaning and results in a complete change of lifestyle, which should imitate Paul's but also the way of life of other biblical figures and of Christ himself.