In recent years, advances in the fabrication of plasmonic nanostructures have pushed the limits of controlling light-matter coupling to the sub-diffraction scale. Applications like surface enhanced Raman spectroscopy, 1 nanolasing, or plasmon assisted photovoltaics harvest the ultra-high electric fields concentrated in tiny mode volumes of the near-field. Placing quantum emitters inside those volumes gives rise to plasmon-exciton coupling with a wide range of coupling strengths. In the weak coupling regime, energy dissipates via decay channels such as Ohmic losses or radiation to the far-field, rather than being transferred back and forth between the subsystems. This regime can be utilized to enhance the emission via the Purcell effect. In the strong coupling regime, the interaction between plasmon and exciton dominates over losses, i.e. plasmon and exciton exchange energy coherently resulting in a splitting of the original resonances into two new polariton modes. Achieving this regime and controlling the energy transfer could allow for intriguing new applications like ultrafast optical switching, quantum networks, or manipulating chemical reactivity. When comparing strong coupling in plasmon-exciton systems to more traditional implementations, e.g. high finesse cavities with trapped atoms, the interesting question arises whether the vast differences in coupling strength and decay rates may lead to qualitatively different features and to potentially new applications.