AbstractBromodomains (BRDs) are small protein domains found in a variety of proteins that recognize and bind to acetylated histone tails. This binding affects chromatin structure and facilitates the localisation of transcriptional complexes to specific genes, thereby regulating epigenetically controlled processes including gene transcription and mRNA elongation. Inhibitors of the bromodomain and extra‐terminal (BET) proteins BRD2–4 and T, which prevent bromodomain binding to acetyl‐modified histone tails, have shown therapeutic promise in several diseases. We report here the discovery of 1,5‐naphthyridine derivatives as potent inhibitors of the BET bromodomain family with good cell activity and oral pharmacokinetic parameters. X‐ray crystal structures of naphthyridine isomers have been solved and quantum mechanical calculations have been used to explain the higher affinity of the 1,5‐isomer over the others. The best compounds were progressed in a mouse model of inflammation and exhibited dose‐dependent anti‐inflammatory pharmacology.