Abstract This paper focuses on factors influencing the duration of buyer–seller relationships. Based on transaction cost economics and relational exchange theory, we discuss key constructs describing long-term relationships and develop hypotheses that can explain differences between long-term and short-term relationships. By using longitudinal data from relationships between Norwegian exporters of farmed salmon and importers in the United States and Japan, we empirically test the relationship duration hypotheses. Our results indicate that relational investments are positively associated with relationship duration; whereas, hierarchical governance mechanisms are negatively associated with relationship duration. Furthermore, the results suggest that governance by relational norms is an important element in designing durable relationships.