An azo compound contains a nitrogen–nitrogen double bond (–N=N–) linking two carbon groups, written R–N=N–R′. When the two groups are aromatic, the N=N unit is conjugated with the rings and absorbs visible light, which is why azo compounds form the basis of a large class of synthetic dyes. They are named with the prefix 'azo-'.

偶氮化合物含有连接两个碳基团的氮氮双键(–N=N–),写作 R–N=N–R′。当两个基团均为芳香族时,N=N 单元与芳环共轭并吸收可见光,因此偶氮化合物构成一大类合成染料的基础。它们以前缀“azo-(偶氮)”命名。