Abstract: Fluorescence and resonance energy transfer (RET) between two chromophores in the presence of nanostructures is a fundamental subject in chemical physics and nanotechnology. My talk includes five parts. First, I would like to give a brief overview of Förster resonance energy transfer and macroscopic quantum electrodynamics (quantization of electromagnetic fields in dielectrics). In the framework of macroscopic quantum electrodynamics, we develop a general theory of RET and establish the concepts of a generalized spectral overlap as well as a coupling factor. Second, we study RET around a metallic nanoparticle and explore the origin of the peaks and the dips of a coupling factor using the general theory we developed. Third, we analyze the mechanisms of RET on a metallic thin film and investigate the distance dependence of RET enhancements. Our theoretical analysis shows that the mechanisms of RET can be separated into mirror dipoles, surface plasmons, and retardation. Fourth, we explore the gap dependence of fluorescence enhancements based on macroscopic quantum electrodynamics and demonstrate the competition between Fluorescence and RET. Fifth, I will show my recent results about quantum dynamics of a molecular emitter strongly coupled with surface plasmon polaritons. The proposed theory allows us to describe the non-Markovian quantum dynamics of a molecular emitter in a wide variety of nanostructures (not limited to plasmonic materials). In a specific condition, we demonstrate an interesting phenomenon called Franck-Condon-Rabi oscillation. (The frequency of Rabi oscillation is dependent on the Franck-Condon factor.). Moreover, we derive a parameter-free formula that can be used to estimate the exciton-polariton coupling between a molecular emitter and a nanocavity and our result is in good agreement with the reported experimental results [Chikkaraddy et al., Nature 535, 127-130 (2016)].