Surface capping plays a critical role in determining the final shape taken by colloidal metals nanocrystals. However, the mechanism is not always clear as it is still a challenging task to even determine the coverage density of capping agents on the final nanocrystals. In this talk, I will use a few examples from our own research to illustrate the critical importance of a quantitative measure of surface capping in understanding the shape evolution of colloidal metal nanocrystals, as well as in predicting the shape evolution process. The examples include bromide ions for the Pd system and poly(vinyl pyrrolidone) for the Ag system. In addition to experimental measurements, computational simulation also offers insightful guidance for the identification of effective capping agents for shape-controlled synthesis.