Diet Pepsi is a no-calorie carbonated cola soft drink produced by PepsiCo, introduced in 1964 as a variant of Pepsi with no sugar. First tested in 1963 under the name Patio Diet Cola, it was rebranded as Diet Pepsi the following year, becoming the first diet cola to be distributed on a national scale in the United States. In the 1960s and 1970s its competition consisted of Tab, produced by The Coca-Cola Company, and Diet Rite cola, produced by RC Cola.

When it was first introduced in 1964, Diet Pepsi was packaged in glass bottles, and was also made available in can format. In 1994, Diet Pepsi became the first product to list a “freshness date” on each individual can and bottle, a practice that would later become a widespread standard in the packaged food and beverage industry. While it was initially advertised alongside Pepsi, Diet Pepsi began to be promoted independently in the late 1960s. Diet Pepsi was also a first in advertising: cross-promotion, e.g., Super Bowl, Top Gun movie, celebrities, Ray Charles, Cindy Crawford, etc. The resulting cross-promotion was the first of its kind, and after it set record videocassette sales, it was described as “the beginning of a trend” by The Los Angeles Times.