6,6-Bicyclic heteroaromatic rings are common scaffolds in drug discovery. This course covers quinoline, isoquinoline, quinoxaline, quinazoline, phthalazine, cinnoline, and the six naphthyridine isomers. It describes some of the methods used to build the rings and touches on their reactivity towards electrophilic substitution, nucleophilic aromatic substitution and palladium catalysed cross-coupling. Classical methods for forming bicycles wherein only one of the two rings contains one or two nitrogen atoms are described, whilst real-life drug discovery projects are used to exemplify the chemistry of the naphthyridines.