To ensure that people only get a mortgage they can afford - and to prevent a recurrence of the irresponsible lending practices of the past - every borrower will now have to prove that they can afford the repayments, both now and in the future.
The FCA has produced a short guide that explains the changes.
About half a million copies will be given out to prospective borrowers in branches of high street lenders, mortgage advisers and estate agents.
“In the past, too many people got a mortgage by simply telling their lender they would have no problem repaying their debt, and that was that,” FCA chief executive Martin Wheatley said.
Getting a mortgage can be one of the biggest financial decisions people will ever make, so it needs careful consideration,” Mr Wheatley said.
“Our new rules will hard-wire common sense into mortgage lending, and the guide we have created will help explain those changes to borrowers.”
The UK mortgage industry has been preparing for the changes for about 18 months and many firms are using the new approach already, the FCA noted.