Reduction of nitrate to nitrite is an integral component of the global denitrification process that is mediated by anaerobic microorganisms in both assimilatory and dissimilatory processes. Due to the unavailability of an established active site structure of the enzyme nitrate reductase, the early model studies mostly spun over the reaction systems containing Mo(iii) and Mo(v) complexes. In the later stage, non-dithiolene-type, N/S/O-donor ligands were employed in order to synthesise realistic model systems, and some of those could reduce nitrate to nitrite. After elucidation of the active site structure of nitrate reductase by X-ray crystallography, the presence of the pyranopterindithiolate ligation to a molybdenum centre prompted the use of ene-dithiolate-type ligands in the model study. Some of the bis(dithiolene) Mo(iv) and W(iv) complexes could react only with proxy substrates, while some other molybdenum complexes cleanly reduced nitrate to nitrite following Michaelis–Menten saturation kinetics and were established as functional models for nitrate reductase activity. These excellent systems for modelling nitrate reductase activity were achieved via a rich legacy of innovative synthetic chemistry by many scientists and spanning more than 30 years of bioinorganic modelling chemistry in the area of mononuclear molybdenum and tungsten enzymes. The present chapter describes this exciting journey.