It is significant to study the characteristics, mechanisms, and maximum earthquake magnitude of injection-induced earthquakes to carry out the work on preventing induced earthquakes, risk assessment, and disaster reduction policy formulation. This study systematically collates the main understandings and disputes on injection-induced earthquakes. The results indicate that geological conditions, such as fault size and stress state, determine the maximum earthquake magnitude. The pressure, cumulative injection volume, and other injection parameters also affect the maximum earthquake magnitude. A reliable way to identify induced earthquakes depends on serious evidence, including spatiotemporal correlation between earthquakes and fluid injection, parameters involved in statistical models, and fault reactivation analysis. When the faults are hydraulically connected to the fluid reservoir, the induce mechanism is commonly attributed to pore-pressure perturbation. Instead, when the fluid pathway is unavailable, the poroelastic stressing may play a dominant role in inducing earthquakes. Aseismic slip, chemical water-rock interaction, and small earthquake interactions also may play essential roles in inducing earthquakes. This study will provide a scientific reference for conducting the inducing mechanism research and promoting the mitigation of destructive disasters caused by induced earthquakes.