ConspectusDeveloping colloidal semiconductor nanocrystals with high-quality optoelectronic properties and precise processability relies on achieving complete mastery over the surface characteristics of nanocrystals (NCs). This requires precise engineering of the ligand-NC surface interactions, which poses a challenge due to the complex reactivity of the multiple binding sites across the entire surface. Accordingly, recent progress has been made by strategically combining well-defined surface models with quantitative surface reactions to advance our understanding and manipulation of NC surface chemistry. Our lab has contributed to this progress by developing a size-dependent shape model of IV-VI NCs, gaining insights into their unique facet-specific chemistry, and developing a systematic ligand modification strategy for target applications. Furthermore, we have created well-defined facets in III-V NCs via a co-passivation strategy, addressing the previously lacking specific shapes.This Account is divided into three parts. First, we discuss the complexities involved in comprehensively understanding the nanocrystal surface structure at the atomistic level. We explain why we focused on well-defined NCs with a large exciton Bohr radius to explore facets, an essential aspect of surface heterogeneity across the entire NC. Second, we present our work on one of the most studied nanocrystals, IV-VI materials, and how facet-specific surface chemistry has led to a meaningful understanding and control of the NC's surface. We discovered a size-dependent facet distribution in IV-VI NCs and suggested facet-specific surface chemistry to improve the photophysical properties of NCs. We further modulate the electronic properties of NC assemblies for efficient optoelectronic applications. Third, we describe our recent success in achieving well-defined facets and their facet-specific chemistry in III-V NCs, which have yet to be explored as much as classical II-VI or IV-VI materials. We explain how controlling the surfaces in III-V NCs has been challenging. We present a precise growth platform for the geometric modulation of NCs, which can be further explored for shape-dependent exciton behavior and surface reactivities.Taken together, we present a compelling case for utilizing facet-specific chemistry as a platform for mechanistic investigation and morphology exploration, which can pave the way for developing high-quality and precisely designed NCs for optoelectronic technologies, unlocking new multidisciplinary applications.