Teams

Currently there are 3 teams in-game: There doesn't seem to be any difference between them apart from colour.
 * Team Mystic (blue)
 * Team Valor (red)
 * Team Instinct (yellow)

After choosing a team you are bound to that team, although there are rumors of this changing in the future.

Team members can work together to neutralize and claim enemy gyms, or level up and protect friendly gyms.