The A3209 is a short A-road in the north of the London Borough of Wandsworth.
The route starts on the Wandsworth Gyratory although the exact spot depends on which map you look at. Some maps give the road its original starting point on the A3 Wandsworth High Street whilst others start the road just to the north where it turns off the gyratory which continues along Armoury Way. Either way, the road heads north along Putney Bridge Road and soon starts to turn westwards.
After running under the railway line west of Clapham Junction station the road runs along the southern edge of Wandsworth Park (whose northern edge is the River Thames). After leaving the park behind, the road goes under another railway bridge, carrying the District Line. A short distance further on, the road ends at traffic lights on the A219 Putney Bridge Road where traffic must turn right in the direction of the bridge.