An electronic commerce system includes a broker that enables customers to purchase items from multiple different merchants. A customer interacts with the merchants to identify items to purchase, and the merchants send descriptions of the items to the broker. The broker maintains a virtual shopping cart that stores the items received from the different merchants. The customer can purchase the items in the shopping cart in a single purchase transaction with the broker. Further, the customer can publish a reference that identifies the shopping cart and invite other customers to purchase the items in the cart via the broker.