Lithium-ion batteries (LIBs) have been extensively used in electronic devices, electric vehicles, and energy storage systems due to their high energy density, environmental friendliness, and longevity. However, LIBs are sensitive to environmental conditions and prone to thermal runaway (TR), fire, and even explosion under conditions of mechanical, electrical, and/or thermal abuse. These unpredictable hazardous consequences significantly limit the commercial applications of LIBs. Thus, these safety issues need to be urgently addressed. In this review, the TR mechanisms and fire characteristics of LIBs are systematically discussed. Battery thermal safety monitoring methods, including the traditional technologies such as temperature, voltage, and gas sensors, as well as the latest new technologies such as optical fiber sensors and ultrasonic imaging, are summarized. A battery thermal management system (BTMS) based on various cooling methods and new insights into the BTMS are briefly presented. According to the fire characteristics of LIBs, nonaqueous and water-based fire extinguishing agents are comprehensively summarized and compared, and the concept of an intelligent fire protection system is discussed. Based on the analysis of the thermal safety issues for preventing possible TRs and for extinguishing an already uncontrollable fire, a complete set of solutions for the thermal safety of LIBs is proposed. In this review, integrated strategies for intelligent detection and fire suppression of LIBs are presented and can provide theoretical guidance for key material design and intellectual safety systems to promote wide application of LIBs.