Customers will be better informed about the speed of their net connection under new rules.
The Ofcom-backed code of practice has won pledges from net firms to give more information about line speeds.
Net firms covering 95% of the UK's broadband users have signed up to the voluntary scheme which comes into force on 5 December.
Over the next six months Ofcom will monitor net firms to ensure they live up to their promises.
The code of conduct was drawn up in response to research that suggested consumers were confused by adverts that promised broadband speeds that few consumers could achieve.
Almost a quarter of people do not get the speed they expect, according to early results from Ofcom research, which is due to be published in full in 2009.
The code requires net firms to: