Nanometric size, nontoxicity, biocompatibility, water solubility paired with efficient, and tunable fluorescence promoted the applications of graphene quantum dots (GQDs) and carbon nanodots (CNDs) in biomedicine, photonics, energy storage, catalysis, and sensing. The combination of easy, low cost, and organic chemistry-based synthesis with surface functionalization and doping further spread the field of potential applications. Modeling of these zero-dimensional (0D) carbon nanomaterials, belonging to the carbon dots family, can provide useful insights into their chemical and physical properties, unveiling, at electronic, atomic, and molecular levels, the mechanisms responsible for their sparkling features. Computational experiments, from quantum chemistry calculations to mesoscale modeling, are fundamental to understand the interaction of GQDs and CNDs with light and matter, to establish the relationship between composition, structure, morphology, optical and electronic features, and to design novel materials and applications. The aim of this chapter is to review the increasing theoretical effort to model GQDs and CNDs and to encourage experimental researchers who synthesize, characterize, and apply 0D carbon nanomaterials to exploit virtual chemistry to obtain molecular insights to tune these amazing systems for novel applications.