Amazon's Product Advertising API, formerly Amazon Associates Web Service (A2S) and before that known as Amazon E-Commerce Service (ECS), is a web service and application programming interface (API) that gives application programmers access to Amazon's product catalog data. Accessible via either the SOAP or REST protocols it enables products to be listed and/or sold through third-party websites and applications. It is a product of Amazon Services, not to be confused with Amazon Web Services.