This article reports the achievement of single-molecule strong coupling at room temperature in plasmonic nanocavities. The researchers developed a method to align isolated methylene-blue molecules within plasmonic nanocavities using host-guest chemistry, enabling strong coupling at room temperature and ambient conditions. By reducing the cavity volume below 40 nm³ and using a nanoparticle-on-mirror (NpOM) geometry, they achieved a strong coupling regime with Rabi frequencies of 300 meV for 10 molecules and 90 meV for single molecules. The results are supported by dispersion curves, vibrational spectroscopy time-series, and dark-field scattering spectra, showing characteristic anticrossings and matching quantitative models. The study demonstrates that the use of plasmonic nanocavities allows for the manipulation of chemical bonds and the exploration of complex natural processes such as photosynthesis. The researchers also show that the Purcell factor for their plasmonic nanocavities is significantly higher than that of state-of-the-art photonic crystal cavities and planar micropillars, indicating strong light-matter coupling. They further demonstrate that single-molecule strong coupling can be achieved by systematically decreasing the number of MB molecules, showing distinct systematic jumps in coupling strength that match the expected increase of g_n from n = 1 - 3 molecules. This provides direct proof of single-molecule strong coupling and shows that the nanocavities can support single-molecule statistics. The study also highlights the potential applications of these nanocavities in various fields, including single photon emitters, photon blockade, quantum chemistry, nonlinear optics, and molecular reactions.This article reports the achievement of single-molecule strong coupling at room temperature in plasmonic nanocavities. The researchers developed a method to align isolated methylene-blue molecules within plasmonic nanocavities using host-guest chemistry, enabling strong coupling at room temperature and ambient conditions. By reducing the cavity volume below 40 nm³ and using a nanoparticle-on-mirror (NpOM) geometry, they achieved a strong coupling regime with Rabi frequencies of 300 meV for 10 molecules and 90 meV for single molecules. The results are supported by dispersion curves, vibrational spectroscopy time-series, and dark-field scattering spectra, showing characteristic anticrossings and matching quantitative models. The study demonstrates that the use of plasmonic nanocavities allows for the manipulation of chemical bonds and the exploration of complex natural processes such as photosynthesis. The researchers also show that the Purcell factor for their plasmonic nanocavities is significantly higher than that of state-of-the-art photonic crystal cavities and planar micropillars, indicating strong light-matter coupling. They further demonstrate that single-molecule strong coupling can be achieved by systematically decreasing the number of MB molecules, showing distinct systematic jumps in coupling strength that match the expected increase of g_n from n = 1 - 3 molecules. This provides direct proof of single-molecule strong coupling and shows that the nanocavities can support single-molecule statistics. The study also highlights the potential applications of these nanocavities in various fields, including single photon emitters, photon blockade, quantum chemistry, nonlinear optics, and molecular reactions.