Research on the molecular mechanism of bacterial flagellar assembly has been an ongoing study that spans three decades. Early work showed that regulation of flagellar gene transcription was coupled to the assembly process. Recent advances in the understanding of the regulation of flagellar assembly have shown that translational and post-translational regulation also plays a significant role in flagellar assembly. In both Salmonella and Caulobacter crescentus, translational regulation influences the secretion of the anti-sigma(28) factor FlgM and the flagellin fljK, respectively. Post-translational regulatory mechanisms also control the length of the hook and the ability of the type III secretion system to discriminate between middle and late secretion substrates. The flagellum provides a model system for understanding how gene regulation functions to ensure the efficient assembly of a complex structure and fundamental mechanisms common to all type III secretion systems.