In A theology of frontier: the Society of Jesus mission towards migrants and refugees, we intend to discuss how the Jesuit concept of frontiers of mission evolved over time and how the Society of Jesus understands it nowadays. First, we studied the history of its General Congregations since Vatican II. Then, we analyzed how Pope Francis s vision of mission, as a Jesuit, influences his ecclesiology. From this point on, we established a parallel between the pope’s missionary choices and those of the Society of Jesus. Due to the urgency of the matter, we focused our analysis only on the work of Jesuits with migrants and refugees, their most dramatic frontier. Pope Francis brought the issue of migrants and refugees to the center of the Church concerns and the Society of Jesus has put special emphasis on their actions with this frontier through the work of the Jesuit Refugee Service (JRS), founded by Father Pedro Arrupe in 1980. For the pope, there is no such thing as a refugee crisis. Actually, according to him, the world is facing a solidarity crisis when men and women refuse to open their doors to their brothers in need. That is why he urges all of us to welcome, protect, promote, and integrate those in need and by doing this replace the globalization of indifference and the politics of rejection and fear by the culture of encounter. Similarly, today, the Society of Jesus understands his mission in this frontier, by means of the work of the JRS, as an offer of hope for those who have been abandoned by all, as an answer to Jesus Christ words I was a stranger and you welcomed me (Mt 25, 35). As a conclusion, we look at the path we have covered in this work from a theological perspective as we try to answer God s question in Genesis 4, 9, Where is your brother?