We study how bundling affects competition between two asymmetric multi-product firms. One firm dominates the other in that it produces better products more efficiently. For low (high) levels of dominance, bundling intensifies (relaxes) price competition and lowers (raises) both firms' profits. For intermediate dominance levels, bundling increases the dominant firm's market share substantially, thereby raising its profit while reducing its rival's profit. Hence, the threat to bundle is then a credible foreclosure strategy. We also identify circumstances in which a firm that dominates only in some markets can profitably leverage its dominance to other markets by tying all its products.Hurkens acknowledges financial support from the Ministry o...