Magnesium and its alloys are the lightest structural metallic materials known, and therefore, hold vast potential for reducing the weight for various transportation modes such as airplanes, cars, buses, etc. Although the alloying of Mg with elements such as Al, Mn, and rare earth elements is known to improve the mechanical properties of Mg, the process is often detrimental to the corrosion performance of Mg. This increase in the corrosion rate occurs because of the microgalvanic couple that forms between the Mg-rich phase, which acts as an anode, and the alloying-element-rich phase, which acts as a cathode. Using both experiments and modeling, it has been reported that the rate of microgalvanic corrosion in the Mg alloys depends on the alloying element and microstructure. However, a deeper understanding is required for quantifying the effect of microstructure characteristics such as the fraction of the two phases, spacing between the two phases, the geometry of the two phases, etc., on the corrosion rate. This understanding is crucial for designing Mg alloys with optimal mechanical properties and high corrosion resistance. To bridge this gap in our understanding, we perform the continuum-scale phase-field modeling of different microstructures observed in Mg alloys. Furthermore, we complement the modeling work with theoretical analysis, where we develop analytical relations for studying the effect of various material and microstructural parameters on the characteristic corrosion length scale. The results from both these efforts will be summarized in our presentation.