A traffic management plan is in effect in Dublin this morning to facilitate road closures for the marathon.
Race organisers are working with the local authorities and the Gardaí to ensure minimum disruption to residents and businesses along the route for the duration of the event.
20,000 people are registered for this year's marathon.
Race Director Jim Aughney says Fitzwilliam Square and Merrion Square have been closed for most of the weekend with other restrictions kicking in this morning.
He said: "About half an hour before the runners are due, the route will close.
"Very soon after the race starts we'll cross North and South Quays and they will be open very quickly after the race passes.
"The N11 will remain open at all times."