The B108 is an urban B-road immediately to the east of the City of London.
It starts in Dalston, at a crossroads with the A104 and A1207, where the former has priority through the junction despite turning off. It heads south along the residential Queensbridge Road crossing a large number of side streets. Eventually the B108 crosses the Regents Canal and then meets the A1208 in Haggerston.
The B108 multiplexes east one block along the A1208 before regaining its number and heading south again. It goes through Bethnal Green before crossing the A11 and A13 in quick succession. It then goes under the LTS railway line and ends on the A1203 in the Wapping Docks area.
In 1922 the northern end of the B108 was on the A1209 in Bethnal Green; it has since been extended northwards.