Boston reached the NBA Finals for the second time in three seasons after defeating Indiana in the Eastern Conference finals.
The Celtics haven't won a title since 2008, when they defeated the Lakers in a six-game series.
They've been methodically developing around young sensation Jayson Tatum and Eastern Conference finals MVP Jaylen Brown.
The Western Conference's Dallas Mavericks defeated the Minnesota Timberwolves in five games to return to the NBA Finals for the first time since 2011, when they won their only title.
Mavs coach Jason Kidd was on that team 13 years ago and now has a chance to win.
Some feared the Mavs' ball-dominant backcourt of Luka Dončić and Kyrie Irving would clash, but the front office has effectively surrounded the All-Star combination with complimentary players.
Dreck Lively III and Jaden Hardy were smart draft picks in the last two seasons and February deals (P.J. Washington, Daniel Gafford) helped Dallas reach the playoffs.
Each franchise built their team differently. Here's how both teams' main players joined.