This review article, published in *Physics of Plasmas* (2024), focuses on the physics of electron emission and electrical breakdown in nanogaps. The authors, Yimeng Li, Lay Kee Ang, Bing Xiao, Flyura Djurabekova, Yonghong Cheng, and Guodong Meng, from various institutions in China, Singapore, and Finland, provide a comprehensive overview of the recent theories, experiments, and atomistic simulations related to these processes. The review begins by highlighting the importance of understanding electron emission and electrical breakdown at the nanoscale due to the miniaturization of electronic devices. It discusses the complete process of electrical breakdown in nanogaps, which includes nano-protrusion growth, electron emission, thermal runaway, and plasma formation. The authors emphasize the transition between different electron emission mechanisms, such as field emission, tunneling, and space-charge limited emission, and the effects of image potential, anode screening, electron space-charge potential, and electron exchange-correlation potential. Experimental findings on electron emission and electrical breakdown in nanogaps are discussed, including the influence of electrode morphology, space-charge effects, and electrical breakdown characteristics. The review also covers advanced atomistic simulations of nano-protrusion growth and thermal runaway under high electric fields. Finally, the authors conclude by outlining key challenges and future perspectives for theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes. They emphasize the need for further research to understand the complex interactions between electron emission, local overheating, and the morphology deformation of nano-protrusions or nanoelectrodes.This review article, published in *Physics of Plasmas* (2024), focuses on the physics of electron emission and electrical breakdown in nanogaps. The authors, Yimeng Li, Lay Kee Ang, Bing Xiao, Flyura Djurabekova, Yonghong Cheng, and Guodong Meng, from various institutions in China, Singapore, and Finland, provide a comprehensive overview of the recent theories, experiments, and atomistic simulations related to these processes. The review begins by highlighting the importance of understanding electron emission and electrical breakdown at the nanoscale due to the miniaturization of electronic devices. It discusses the complete process of electrical breakdown in nanogaps, which includes nano-protrusion growth, electron emission, thermal runaway, and plasma formation. The authors emphasize the transition between different electron emission mechanisms, such as field emission, tunneling, and space-charge limited emission, and the effects of image potential, anode screening, electron space-charge potential, and electron exchange-correlation potential. Experimental findings on electron emission and electrical breakdown in nanogaps are discussed, including the influence of electrode morphology, space-charge effects, and electrical breakdown characteristics. The review also covers advanced atomistic simulations of nano-protrusion growth and thermal runaway under high electric fields. Finally, the authors conclude by outlining key challenges and future perspectives for theoretical, experimental, and atomistic simulation studies of nanoscale electrical breakdown processes. They emphasize the need for further research to understand the complex interactions between electron emission, local overheating, and the morphology deformation of nano-protrusions or nanoelectrodes.