Toluene diisocyanate (TDI) is an organic compound with the formula CH3C6H3(NCO)2. Two of the six possible isomers are commercially important: 2,4-TDI (CAS: 584-84-9) and 2,6-TDI (CAS: 91-08-7). 2,4-TDI is produced in the pure state, but TDI is often marketed as 80/20 and 65/35 mixtures of the 2,4 and 2,6 isomers respectively. It is produced on a large scale, accounting for 34.1% of the global isocyanate market in 2000, second only to MDI.

Toluene diisocyanate exists in two isomeric forms (2,4-toluene diisocyanate and?2,6-toluene diisocyanate) which have similar properties and effects. Toluene diisocyanate is produced commercially as an 80:20 (2,4-toluene diisocyanate:2,6-toluene diisocyanate) mixture of the two isomers.