Firm heterogeneity theory provides a framework within which to explain how firms become involved in international trade. Export entry incurs a fixed cost and only firms that are highly productive can self-select into foreign markets. This research examines the importance of firm characteristics on export performance, taking Laos as a case study. The findings suggest that firms that are larger, have capable managers, and that are in ventures with foreign partners are more productive and more likely to export and to participate in international production networks. Economies of scale and international linkages appear to play key roles in allowing firms to overcome the initial costs of entry into foreign markets.