Hub-and-spoke arrangements involve coordination between competitors (spokes) through a common intermediary (hub), such as a supplier or retailer. Information exchange between the competitors is indirect through the hub. This raises antitrust issues if legitimate conversations between the hub and spokes are used to facilitate anti-competitive coordination between horizontal competitors. Enforcement authorities must determine if inherently legal vertical discussions have been used for illegal horizontal collusion and distinguish between legal vertical agreements and illegal hub-and-spoke arrangements.