Strong coupling between surface plasmon polaritons (SPPs) and quantum emitters is a key topic in modern physics. This review explores the concepts and recent advances in the strong coupling of SPPs with quantum emitters such as excitons in J-aggregates, dye molecules, and quantum dots. The phenomenon of strong coupling involves the hybridization of energy levels between the emitter and the local optical environment, leading to new modes with frequencies different from those of the original oscillators. The strong coupling regime is characterized by the Rabi splitting, which is the energy separation between the new normal modes. This regime is defined by the coupling strength being large compared to the linewidths of the coupled systems. Strong coupling is important in various fields of physics and technology, including light-matter interactions, quantum information processing, and nanophotonics. The coupling between SPPs and emitters is particularly interesting due to the extensive control over plasmon modes supported by metallic nanostructures. This control is achieved through advanced nano-fabrication techniques and a deep understanding of the relationship between nanostructure details and plasmon modes. The review discusses the basics of strong coupling using the example of two coupled harmonic oscillators. The dynamics of the coupled system are described by differential equations that can be solved to give the time evolution of the positions of the oscillators. The new frequencies that appear are the normal modes of the coupled system, which are hybrids of the original modes. The strength of the coupling determines the energy separation between these modes. The review also explores the relevance and applications of strong coupling, including its role in coherence phenomena, stimulated emission, gain, and lasing. Strong coupling has been observed in various systems, including atoms in cavities, organic semiconducting materials, and superconducting circuits. The ability to modify the electromagnetic environment of an emitter through strong coupling has been used to control chemical reactions and modify chemical landscapes. The review highlights the importance of strong coupling in the context of surface plasmon polaritons and emitters. SPPs are hybrid modes involving electron oscillations in a metal and an oscillating light field on the metal surface. Their near-field character allows for the confinement of light to dimensions smaller than the free-space wavelength, enabling nano-optics and applications such as surface-enhanced Raman spectroscopy and biosensing. The strong coupling of SPPs with emitters has been demonstrated for various types of emitters, including J-aggregates, dye molecules, and quantum dots. The review also discusses the experimental and theoretical developments in the field of strong coupling, including the use of different coupling schemes such as prism coupling, grating coupling, and near-field coupling. The role of the local optical density of states in resonant energy transfer is still a topic of debate. The review concludes with a perspective on the future of this rapidly emerging field, emphasizing its potential for further exploration and application in various areas of science.Strong coupling between surface plasmon polaritons (SPPs) and quantum emitters is a key topic in modern physics. This review explores the concepts and recent advances in the strong coupling of SPPs with quantum emitters such as excitons in J-aggregates, dye molecules, and quantum dots. The phenomenon of strong coupling involves the hybridization of energy levels between the emitter and the local optical environment, leading to new modes with frequencies different from those of the original oscillators. The strong coupling regime is characterized by the Rabi splitting, which is the energy separation between the new normal modes. This regime is defined by the coupling strength being large compared to the linewidths of the coupled systems. Strong coupling is important in various fields of physics and technology, including light-matter interactions, quantum information processing, and nanophotonics. The coupling between SPPs and emitters is particularly interesting due to the extensive control over plasmon modes supported by metallic nanostructures. This control is achieved through advanced nano-fabrication techniques and a deep understanding of the relationship between nanostructure details and plasmon modes. The review discusses the basics of strong coupling using the example of two coupled harmonic oscillators. The dynamics of the coupled system are described by differential equations that can be solved to give the time evolution of the positions of the oscillators. The new frequencies that appear are the normal modes of the coupled system, which are hybrids of the original modes. The strength of the coupling determines the energy separation between these modes. The review also explores the relevance and applications of strong coupling, including its role in coherence phenomena, stimulated emission, gain, and lasing. Strong coupling has been observed in various systems, including atoms in cavities, organic semiconducting materials, and superconducting circuits. The ability to modify the electromagnetic environment of an emitter through strong coupling has been used to control chemical reactions and modify chemical landscapes. The review highlights the importance of strong coupling in the context of surface plasmon polaritons and emitters. SPPs are hybrid modes involving electron oscillations in a metal and an oscillating light field on the metal surface. Their near-field character allows for the confinement of light to dimensions smaller than the free-space wavelength, enabling nano-optics and applications such as surface-enhanced Raman spectroscopy and biosensing. The strong coupling of SPPs with emitters has been demonstrated for various types of emitters, including J-aggregates, dye molecules, and quantum dots. The review also discusses the experimental and theoretical developments in the field of strong coupling, including the use of different coupling schemes such as prism coupling, grating coupling, and near-field coupling. The role of the local optical density of states in resonant energy transfer is still a topic of debate. The review concludes with a perspective on the future of this rapidly emerging field, emphasizing its potential for further exploration and application in various areas of science.