In marketing a coupon is a ticket or document that can be exchanged for a financial discount or rebate when purchasing a product. Customarily, coupons are issued by manufacturers of consumer packaged goods or by retailers, to be used in retail stores as a part of sales promotions. They are often widely distributed through mail, magazines, newspapers, the Internet, and mobile devices such as cell phones.

Origin
In 1887, the Coca-Cola Company was incorporated with Asa Candler as one of the partners. He transformed Coca-Cola from an insignificant tonic into a profitable business by using innovative advertising techniques. The key to this growth was Candler's ingenious marketing including having the company's employees and sales representatives distribute complimentary coupons for Coca-Cola. Coupons were mailed to potential customers and placed in magazines. The company gave soda fountains free syrup to cover the costs of the free drinks. It is estimated that between 1894 and 1913 one in nine Americans had received a free Coca-Cola, for a total of 8,500,000 free drinks. By 1895 Candler announced to shareholders that Coca-Cola was served in every state in the United States.

History
Coupons first saw widespread use in the United States in 1909 when C. W. Post conceived the idea to help sell breakfast cereals and other products. Today, more than 700 corporations offer coupons for discounts on products or services. Each year, coupons for consumer packaged goods generate nearly 3 billion dollars in transactions within the U.S. alone.

There are many different types of online coupons such as discounts, free shipping, first-time customer coupons, and free giveaways.

Internet coupons
Online retailers often refer to Internet coupons as "coupon codes," "promotional codes," "promotion codes," "discount codes," "key codes," "promo codes," "surplus codes," "portable codes," "shopping codes," "voucher codes," or "source codes." Internet coupons typically provide for reduced cost or free shipping, a specific dollar or percentage discount, or some other offer to encourage consumers to purchase specific products or to purchase from specific retailers.

Taxation
Depending on the jurisdiction, coupons may or may not reduce the sales tax which must be paid by the consumer. This is often determined by who sponsors the coupon. If the coupon is issued by the retailer, the product was never offered at the original price and the coupon represents a reduction in the amount paid and the tax. If the coupon is issued by the manufacturer, the original price is still paid but some of the price is covered by the manufacturer instead of the consumer and the full price remains taxable. This is the case with the coupon-eligible converter boxes in the U.S., which compensate in part for the forced conversion to digital TV.