The R821 road is a regional road in south Dublin, Ireland.

The road starts at the junction with the R115 (Willbrook Road) in Rathfarnham and passes through Nutgrove before terminating at Churchtown.

A westbound bus lane is present along the entire route while after Nutgrove there is also a bus lane heading east until the end of the route in Churchtown.

There are a number of Dublin Bus routes along the R821: There is an off street bike lane on the route though there are a few sections where the lane ends unexpectedly.

Currently there are plans to upgrade the junction with the R112 and Beaumont Avenue.