It was also the 86th season of FIFA-sanctioned soccer in the United States, and the 20th with a national first-division league.
The Chicago Fire and Miami Fusion played their inaugural seasons as the league's first two expansion teams.
The season began on March 15 and concluded with MLS Cup on October 25.
The conference semifinals and finals were played as a best-of-three series, and the winners advanced to MLS Cup.
The team with the most points in the regular season was awarded the MLS Supporters' Shield and qualified automatically for the CONCACAF Champions' Cup.