This paper examines the causal relationship between exporting and productivity using firm-level panel data from Colombia, Mexico, and Morocco. The authors analyze whether firms become more efficient after becoming exporters and whether exporters generate positive spillovers for domestically-oriented producers. They model the decision to export as a dynamic optimization problem, considering sunk start-up costs and potential learning effects. The results show that relatively efficient firms tend to become exporters, but their unit costs are not affected by previous export market participation. This suggests that the efficiency gap between exporters and non-exporters is due to self-selection rather than learning by exporting. Additionally, while exporters may reduce the costs of breaking into foreign markets for domestic producers, they do not significantly improve these producers' efficiency. The paper also finds some evidence of external benefits for exporters in export-intensive industries or regions, but no significant productivity gains. The findings are supported by econometric tests, which confirm that past export market participation does not influence current costs.This paper examines the causal relationship between exporting and productivity using firm-level panel data from Colombia, Mexico, and Morocco. The authors analyze whether firms become more efficient after becoming exporters and whether exporters generate positive spillovers for domestically-oriented producers. They model the decision to export as a dynamic optimization problem, considering sunk start-up costs and potential learning effects. The results show that relatively efficient firms tend to become exporters, but their unit costs are not affected by previous export market participation. This suggests that the efficiency gap between exporters and non-exporters is due to self-selection rather than learning by exporting. Additionally, while exporters may reduce the costs of breaking into foreign markets for domestic producers, they do not significantly improve these producers' efficiency. The paper also finds some evidence of external benefits for exporters in export-intensive industries or regions, but no significant productivity gains. The findings are supported by econometric tests, which confirm that past export market participation does not influence current costs.