This Master's thesis analyzes the concept of unity in the theology of Dumitru Stăniloae, one of the most prominent Orthodox theologians of the 20th century. Anchored in textual analysis, it examines Stăniloae's theological assertions on unity and their relevance for ecumenical ecclesiological discussions. Stăniloae's notion of the Church's catholicity, termed “open sobornicity,” is explored and expanded into the concept of “open unity,” highlighting its potential to enrich ecumenical dialogues. Methodologies employed include textual analysis, contextual reading, and theological reflection. The study's findings reveal that Stăniloae's theology not only enriches the Orthodox tradition but also offers a robust framework for inter-Christian and interreligious dialogue. It underscores the crucial role of openness towards others and emphasizes the importance of ecological sensitivity and harmonious coexistence in unity within entire creation.