Consultation on plans for a third runway and new terminal begins on Tuesday and closes on September 13.
It will be staging more than 40 public exhibitions as well as other events and leafleting.
Heathrow will use the responses to frame its planning application which is expected to go in next summer.
It will also consult on its proposal to bring in up to 25,000 extra flights per year in advance of a third runway opening.
Heathrow hope to have the new runway open by 2026.