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Celtics' dominance, league expansion and competition (1956–1979)

In 1957, rookie center Bill Russell joined the Boston Celtics, which already featured guard Bob Cousy and coach Red Auerbach, and went on to lead the franchise to eleven NBA titles in thirteen seasons. Center Wilt Chamberlain entered the league with the Warriors in 1959 and became a dominant individual star of the 1960s, setting new single-game records in scoring (100) and rebounding (55). Russell's rivalry with Chamberlain became one of the greatest rivalries in the history of American team sports.

The 1960s were dominated by the Celtics. Led by Russell, Cousy, and Auerbach, Boston won eight straight championships in the NBA from 1959 to 1966. This championship streak is the longest in the history of American professional sports. They did not win the title in 1966–67, but regained it in the 1967–68 season and repeated in 1969. The domination totaled nine of the ten championship banners of the 1960s.

Through this period, the NBA continued to evolve with the shift of the Minneapolis Lakers to Los Angeles, the Philadelphia Warriors to San Francisco, the Syracuse Nationals to Philadelphia to become the Philadelphia 76ers, and the St. Louis Hawks moving to Atlanta, as well as the addition of its first expansion franchises. The Chicago Packers (now Washington Wizards) became the ninth NBA team in 1961. From 1966 to 1968, the league expanded from 9 to 14 teams, introducing the Chicago Bulls, Seattle SuperSonics (now Oklahoma City Thunder), San Diego Rockets (who moved to Houston four years later), Milwaukee Bucks, and Phoenix Suns.

In 1967, the league faced a new external threat with the formation of the American Basketball Association (ABA). The leagues engaged in a bidding war. The NBA landed the most important college star of the era, Kareem Abdul-Jabbar (then known as Lew Alcindor), who went on to become the league's best player of the 1970s. However, the NBA's leading scorer, Rick Barry, jumped to the ABA, as did four veteran referees— Norm Drucker, Earl Strom, John Vanak, and Joe Gushue.

In 1969, Alan Siegel, who oversaw the design of Jerry Dior's Major League Baseball logo a year prior, created the modern NBA logo inspired by the MLB's. It incorporates the silhouette of Jerry West, based on a photo by Wen Roberts. The NBA would not confirm that a particular player was used because, according to Siegel, "They want to institutionalize it rather than individualize it. It's become such a ubiquitous, classic symbol and focal point of their identity and their licensing program that they don't necessarily want to identify it with one player." The logo debuted in 1971 (with a small change to the typeface on the NBA wordmark in 2017) and would remain a fixture of the NBA brand.

The ABA succeeded in signing a number of major stars in the 1970s, including Julius Erving of the Virginia Squires, in part because it allowed teams to sign college undergraduates. The NBA expanded rapidly during this period. From 1966 to 1974, the NBA grew from nine franchises to 18. In 1970, the Portland Trail Blazers, Cleveland Cavaliers, and Buffalo Braves (now the Los Angeles Clippers) all made their debuts expanding the league to 17. The New Orleans Jazz (now in Utah) came aboard in 1974 bringing the total to 18. Following the 1976 season, the leagues reached a settlement that provided for the addition of four ABA franchises to the NBA, raising the number of franchises in the league at that time to 22. The franchises added were the San Antonio Spurs, Denver Nuggets, Indiana Pacers, and New York Nets (now the Brooklyn Nets). Some of the biggest stars of this era were Abdul-Jabbar, Barry, Dave Cowens, Erving, Elvin Hayes, Walt Frazier, Moses Malone, Artis Gilmore, George Gervin, Dan Issel, and Pete Maravich. The end of the decade, however, saw declining TV ratings, low attendance and drug-related player issues – both perceived and real – that threatened to derail the league.