Diethylphosphite or DEPI  is a colorless liquid. It is a versatile reactive intermediate used in the production of various phosphorus based substances.

It has got major applications as an intermediate in the pharmaceutical industryand in flame retardants.

It also has some commercial applications and industrial uses as paint solvent, lubricant Plastic Additive, antioxidant for plastics, reducing agent, agrochemicals and canbe used in plasticizers and extracting agents.