For the past 30 years, in addition to the standard boxes of coloured bricks that made it famous, LEGO has produced a large number of "themes": grouped collections of conceptually related playsets devoted to a specific setting or concept. The multitude of themes have explored a vast array of different time periods, settings, genres, themes, and even styles of building. As you may have guessed by now, this is an index of said themes.
LEGO System (basic bricks) original themes (and debut year)
Advanced build themes
Buildable Action Figures (original themes only)
Licensed LEGO themes
Board Games (not including board games based on licensed themes)