This book clearly presents a fully modified theory on Coulomb excitations/decays in graphene-related systems, in which the theoretical framework combines layer-dependent random-phase approximation (RPA) and the generalized tight-binding model. It can deal with a plenty of critical factors related to different lattice symmetries, layer numbers, dimensions, stacking configurations, orbital hybridizations, intralayer & interlayer hopping integrals, spin-orbital couplings, temperatures, electron/hole dopings, electric field, and magnetic field. Apparently, there exist rich and unique electronic excitation phenomena due to the distinct energy bands and wave functions in various condensed-matter systems, as obviously revealed in the diverse (momentum, frequency)-phase diagrams. The calculated results, with the concise physical pictures, clearly illustrate the important roles of electron-electron (e–e) Coulomb interactions. Of course, they could explain the up-to-date experimental measurements. This model could be generalized to other emergent 2D materials under detailed calculations/investigations, such as the layered silicene [34,132,152,387], germanene [154,238], tinene [494], phosphorene [29], antimonene [29], bismuthene [29, 389], and MoS2 [29]. Further studies would provide significant differences among these systems and be useful in thoroughly understanding the close/complicated relations of essential physical properties. On the other hand, the theoretical models should be derived again to solve Coulomb excitations in 1D and 0D systems without good spatial translation symmetry [124,126,126,348,428-430]. For example, 1D graphene nanoribbons and 0D graphene quantum dots have open boundary conditions, so that they, respectively, possess many energy subbands and discrete energy levels. Maybe, the dielectric function tensor, being characterized by the subband/level index, is an effective way to see the excitation properties [350].