Over the past two decades microstructurally refined materials have garnered attention due to the unique properties that result from grain refinement, namely possible improvements in strength and wear resistance. However, there has been limited work on developing a fundamental understanding of how such grain refinement and more generally how grain size affects the corrosion resistance of an alloy. What work has been presented in the literature is often contradictory, indicating that grain refinement both can improve and be detrimental to an alloys' corrosion resistance depending on the specific alloy under study. A review of previous work on the relationship between grain size and corrosion resistance including critical considerations will be presented for Ti, Cu, Al, and Mg alloy systems. Additionally, preliminary results from a study using high purity aluminium (99.999%) aimed at isolating the microstructural effects of grain size on corrosion from the effects of alloying additions will be presented.