Thiodiglycol, or bis(2-hydroxyethyl)sulfide (also known as 2,2-thiodiethanol or TDE), is the organosulfur compound with the formula S(CH2CH2OH)2.

It is used as a solvent in a variety of applications ranging from dyeing textiles to inks in some ballpoint pens.

In chemical synthesis, it is used as a building block for protection products, dispersants, fibers, plasticizers, rubber accelerators, pesticides, dyes, and various other organic chemicals.

The ability to vary the refractive index of the medium by varying the concentration of TDE in an aqueous solution, plus its relative lack of toxicity makes it highly desirable for such use.

Thiodiglycol is also a product of the hydrolysis of the "mustard gas" bis(2-chloroethyl)sulfide and can be detected in the urine of casualties.