The Byzantine Empire maintained diplomatic contacts with the West in various ways, but the paper analyzes the negotiated and concluded marriage alliances between the ruling members of the imperial family in Constantinople and influential families in the medieval Europe until 1204. Candidates who were intended for marriage with Western dignitaries came directly from the imperial family and with their entourage influenced the development of new customs and cults in the West. Marriage proposals are observed through a religious and political prism. Despite stereotyping, there is an exchange in the cultural, artistic and scientific fields, which represents a positive achievement of the marriage policy. The number of achieved marriages depends on how decadent the Empire's power was, how much the ruling emperor was pro-Western oriented and how was he ready to seal an alliance that would bring him the expected help in difficult times. During the XIIth century, a large number of marriages were concluded due to political pressure, which had a long-term effect on the internal and external political stability of the Empire.