Authorize.Net is a popular payment gateway service provider allowing merchants to accept credit card and electronic check payments.
Using such a gateway to issue a one-time transactions doesn't raise any great troubles, but serving returning customers or managing complex subscriptions requires you either to be compliant with the Payment Card Industry Data Security Standard (PCI DSS) or to ask your customer to re-enter his or her billing info every time. Neither is always what you want. Well, among other Authorize's features there is a Customer Information Manager (CIM), which targets that particular problem.