The present paper examines multi‐product exporters in Belgium, considering their importance and the relationship between the margins of trade and firm productivity. We use proxies for trade costs to quantify the extensive and intensive margin adjustments of trade. Relatively few exporting firms account for the majority of Belgian exports and these large firms have greater productivity and value‐added, more employees and more exported products than smaller exporters. Across firms, productivity is positively associated with firm exports. More productive firms export more products to more countries and have higher average product‐country export flows. The extensive and intensive margins are equally important in total firm exports.