Ethnic, cultural, and value diversity in multicultural societies requires adaptive intercultural communication to maintain social harmony. This study aims to analyze the patterns of intercultural communication between Minangkabau and Javanese communities in Nagari Bancah Kariang, Pasaman Barat Regency, and to identify supporting factors and their contributions to social harmony. The research employs a descriptive qualitative approach using a case study method. Data were collected through observation, interviews, and documentation, and analyzed through data reduction, data display, and conclusion drawing using triangulation techniques to ensure data validity. The findings indicate that intercultural communication occurs dynamically, adaptively, and contextually. The convergence communication pattern is dominant, characterized by adjustments in language, intonation, speech tempo, and communicative attitudes, with Indonesian serving as a unifying language. Meanwhile, divergence patterns appear situationally as expressions of cultural identity without disrupting social harmony. Communication adjustment involves not only linguistic aspects but also communication ethics such as politeness and respect for other cultural norms. This study concludes that social harmony is not formed spontaneously but through continuous communication processes and a balanced social system. Accommodation Communication Theory explains communication adjustments at the micro level, while Structural Functional Theory through the AGIL concept explains the sustainability of the social system at the macro level. These two approaches complement each other in explaining the dynamics of intercultural communication and its contribution to harmony in a multiethnic society.