The Celtics were formed in 1946 as a team in the Basketball Association of America. After the merger of the BAA and the National Basketball League to form the National Basketball Association, the Celtics acquired rookie Bill Russell in 1956. Russell had an immediate impact; that year, the Celtics advanced to the NBA Finals and defeated the then St. Louis Hawks in seven games, giving the Celtics the first of a record 16 NBA Championships. In 1957, the Celtics again advanced to the NBA Finals, this time losing to the Hawks in 6 games. However, with the acquisition of K.C. Jones, the Celtics began a dynasty that would last 8 seasons.

In 1959, with Russell and Jones, the Celtics won the NBA Championship with the sweep of the Minneapolis Lakers. Under coach Red Auerbach, the Celtics won another seven championships for eight championships in a row. During that timespan, the Celtics met the Lakers in the Finals six times, starting an intense- and sometimes bitter- rivalry. The Celtics would eventually meet the Lakers a total of 10 times in the NBA Finals. After the 1966 championship, though, Auerbach retired. Russell took over as a player and coach. However, that year the Celtics' string of NBA titles was broken. The aging team managed two more championships, though, in 1968 and 1969, each against the Lakers in the NBA Finals. Russell retired after the 1969 season, effectively ending a dominant Celtics dynasty that had garnered 11 NBA titles. The streak of 8 consecutive NBA championships is the longest streak of consecutive championships in U.S. sports history.

The next season was one of rebuilding as the Celtics had their first losing record in a long time. However, with Dave Cowens, Paul Silas, and Jo Jo White, the Celtics became dominant again. In 1974 the team bested the Milwaukee Bucks in the NBA Finals, and in 1976 the team won yet another championship after defeating the Phoenix Suns. After the 1976 victory, though, Boston went into another phase of rebuilding.

The rebuilding phase only lasted two years. With the acquisition of NBA legend Larry Bird, Robert Parish, and Kevin McHale, the Celtics yet again became a dominant team in the NBA, playing in 5 NBA Finals in the 1980s. The team won a title in 1981, and the following year K.C. Jones was named head coach. Jones led the Celtics to four consecutive NBA Finals appearances against the Lakers and the Houston Rockets between 1984 and 1987, winning championships in 1984 and 1986. The three Finals where the Celtics played the Lakers featured the matchup of Bird versus NBA great Magic Johnson.

After the retirement of Bird, the Celtics yet again went into rebuilding. In 1994 the Celtics moved from the Boston Garden into the Fleet Center. Under current general manager Danny Ainge and coach Doc Rivers, the Celtics won the division championship in the 2004-2005 season, but lost to the Indiana Pacers in game 7 in the postseason. As of 2005 the Celtics are the only team in NBA history to have never lost a Game 7 in the NBA Finals. They are a perfect 7-0 in these games, winning in 1957, 1960, 1962, 1966, 1969, 1974, and 1984.

--Wikipedia