From the decades immediately following its foundation in 1540, the Society of Jesus was involved by the Roman Curia in the development of a missionary project aimed at supporting Catholic communities along the predominantly Catholic Dalmatian coast, and in the European provinces of the Ottoman Empire. Beyond the borders of Christendom, the Balkan missions took shape in a territory under Ottoman sovereignty characterized by a highly diverse confessional landscape, far removed both from colonial settings and from the Jesuit experiences in the great Asian empires. Lacking firm and continuous political protection, the Jesuits acted as a presence institutionally tolerated by the Ottoman system, developing strategies of adaptation to ensure the continuity of pastoral activity in a land perceived as a limb of Christian Europe usurped by the "Turk." These strategies, however, emerged within a network of asymmetrical relationships: on the one hand, between missionaries and Ottoman authorities, who exercised discretionary control over their presence, movements, and permitted religious practices; on the other, between the Jesuits themselves and other Catholic actors - such as merchants, diplomats and other religious orders - active in the Adriatic and Balkan regions. Through the analysis of missionary correspondence, reports sent to Rome, and Jesuit autobiographical writings, this paper presents the tensions that ran through the Society's missions in south-eastern Europe—from internal conflicts within the Catholic world to shifting relations with Ottoman authorities and the Orthodox clergy. It shows how, between the second half of the sixteenth century and the first half of the seventeenth, the Ottoman Balkans became a true missionary laboratory and a space of intersection, where adaptation, negotiation, and confessional discipline intertwined with the changing balance of power between European states and the Sublime Porte.