This study presents the first comprehensive analysis of Seventhday Adventist interchurch relations -- a 20-million-member body whose ecumenical stance has so far been under-researched. For the sake of interpreting denominational involvement and reservations in Adventism as well as beyond, the study develops a new academic approach to ecumenism based on Relational Models Theory, a comprehensive social science paradigm of interpreting human relationships. The resulting typology of ecumenical interactions and the historical case study of Adventism suggest that such a relational interpretation of ecumenical interaction sheds light on many of the unresolved issues in ecumenics -- such as divergent concepts of unity, difficulties in recognition processes, and the permanence of denominationalism.