A product catalog service allows business entities to create and store product catalogs indicating products that are available from the business entities. A product catalog includes multiple product family definitions. Each product family definition specifies attribute names of a product family and, for each attribute name, a set of allowed attribute values. In order to specify a particular product variant, an entity may supply one of the allowed attribute values for each specified attribute name of the product. The product catalogs may be received from multiple business entities. Each product catalog may also be shared with multiple business entities. A merchant, for example, may select products from a product catalog to purchase from another merchant. When creating a product catalog, a business entity may reference product family definitions of other product catalogs.