A subscription business model is a model in which a customer must pay a recurring price at regular intervals for access to a product or service. Subscriptions give companies consistent revenue from customers during a long-time payment for a service depending on usage. For many companies, the most important aspect is a customer retention. Subscriptions convert a customer into a subscriber, and these customers are inclined to buy again. Renewal of subscriptions may be activated automatically so that the cost is automatically paid for by a pre-authorized charge. From a marketing perspective, subscriptions have the added benefit that vendors know the number of currently active members since a subscription typically involves a contractual agreement.