The Junior TT is a motorcycle road race that takes place during the Isle of Man TT festival; an annual event at the end of May and beginning of June. Between 1949 and 1976 this race was part of the Grand Prix motorcycle racing season.

The 1911 Isle of Man TT was the first time the Junior TT race took place and was open to 300cc single-cylinder and 340cc twin cylinder motor-cycles and was contested over 5 laps of the new 37.5 mile Mountain Course. The first event on the new course was the Junior TT Race and was contested by 35 entrants. It was won by Percy J. Evans riding a Humber motorcycle in 3 hours, 37 minutes and 7 seconds at an average speed of 41.45 mph.

The 1912 event was the first to limit the Junior TT to only 350 cc machines and this engine capacity prevailed until 1994.

The 2012 specification for entries into the Junior TT race are defined as;-

The lap record for the Junior TT is 17 minutes and 31.328 seconds, at an average speed of 129.197 mph (207.922 km/h) set by Michael Dunlop on lap 2 of the 2018 Isle of Man TT 600cc Supersport Junior TT Race 1. The race record for a four-lap Junior TT is 1 hour, 11 minutes and 28.059 seconds at an average race speed of 126.703 mph (203.909 km/h) set by Dean Harrison during the 2018 600cc Supersport TT Race 2.