Former President Bill Clinton will deliver the keynote address on opening day of the U.S. Green Building Council’s Greenbuild conference and exposition, Nov. 7-9, in Chicago.

Clinton’s speech will kick off what the USGBC expects to be the largest Greenbuild ever. The council says more than 20,000 people from all over the world are expected to take part in the three-day event. Greenbuild’s exhibit hall sold out nearly a year in advance with 800 booths.