Diazine refers to a group of organic compounds having the molecular formula C₄H₄N₂. Each contains a benzene ring in which two of the C-H fragments have been replaced by isolobal nitrogen. There are three isomers:

• pyrazine (1,4-diazine)
• pyrimidine (1,3-diazine)
• pyridazine (1,2-diazine)