Amazon Marketplace Web Service (Amazon MWS) is a Web service API that can help Amazon sellers automate processes for listings, orders, payments, reports, and more.
Amazon listing, order, and payment data can be integrated into existing workflows so that selling on Amazon fits right in with your regular business practices.
The Amazon MWS portal has client libraries, comprehensive documentation, and lots more. Take a look around: https://developer.amazonservices.com
If you like what you see when you explore the site, sign up before you leave by clicking the "Sign up for MWS" button on the home page.