In the group of energetic diazoles, 4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (TNBI) have attracted much attention in the past few years. Although the compound suffers from hygroscopicity, it is a useful substrate for the synthesis of new high energy materials. The review summarizes published data on the methods of preparation, structure, properties and energetic characteristics of TNBI, its salts and N-substituted derivatives. This class of compounds contains mainly nitrogen rich molecules with potential to become future propellants and explosives.