Azo compounds are organic compounds. The name "azo" refers to a functional group demonstrated by two nitrogen bonds linked by a double bond.
Azo compounds were first discovered in the 1800's by a scientist named Greiss. Diazotation was discovered in 1858 and the coupling of azo salts to produce dyes, in 1864.
There are huge numbers of different types of azo compounds, each with a different use. They are used as dyestuffs, in clothing, food colourings, such as Bismark Brown used as colouring in kippers, and indicators in chemical processes, for example, methyl-orange which is used as an acid-base indicator.