Thermal runaway incidents involving lithium-ion batteries (LIBs) occur frequently and pose a considerable safety risk. This comprehensive review explores the characteristics and mechanisms of thermal runaway in LIBs as well as evaluation methods and possible countermeasures. First, the characteristics of, factors influencing, and mechanisms underlying thermal runaway in LIBs are examined in detail. Second, thermal runaway propagation is explored. The characteristics and formation mechanisms of the products of thermal runaway such as flames, gases, and solids are also explored. The thermal hazards associated with toxic products, high temperature, smoke, pressure shocks, combustion, and explosions must be appropriately prevented. Therefore, multiparameter evaluation methods for assessing the risk of thermal runaway in LIBs are discussed. Finally, this review details various countermeasures for controlling or preventing thermal runaway in LIBs. Overall, although inherently safe LIBs can be developed, suitable warning systems, thermal runaway suppression materials, and fireextinguishing systems are valuable for thermal runaway management.