The element vanadium (V) has been applied to challenges spanning Earth and Environmental Sciences. It is a critical metal, with industry applications in next generation batteries and as a steel alloy. It has rich redox chemistry with multiple oxidation states, prompting decades of oxygen fugacity (fO2) proxy development at high and low temperatures, on Earth and other planets. Some organisms even employ V in place of iron to carry oxygen in their bloodstreams. However, vanadium, in its 5+ oxidation state is also highly toxic and is increasing recognised as a potentially serious environmental pollutant. The isotopic composition of vanadium can be applied to investigate all of the above scenarios. The first method to measure V isotopes to a precise useful for Earth and environmental science applications was developed in the Earth Science department at Oxford circa 2009. In this seminar, I will discuss how that analytical development unfolded, and how the applications of vanadium isotopes have evolved from initial lofty ambitions of a direct fO2 proxy in magmatic systems to current potential breakthroughs in environmental pollutant tracing.