Abstract: N-type Mg₃Sb₂-based thermoelectric materials combine competitive thermoelectric performance with low raw material costs, demonstrating considerable potential for power generation and cooling applications. However, their practical implementation is constrained by several stability challenges. At elevated temperatures, Mg readily volatilizes and diffuses, while humid environments induce selective corrosion of Mg. During device assembly and joining, elemental interdiffusion, interfacial reaction layer growth, and accumulated thermal stress progressively degrade thermoelectric output, potentially leading to cracking and device failure. Consequently, stability has emerged as a major obstacle to the practical deployment of N-type Mg₃Sb₂-based thermoelectrics. This review first outlines the crystal structure, electrical transport characteristics, and Mg-defect thermodynamics of these materials. It then summarizes recent advances in high-temperature thermal stability, environmental stability, and device interface reliability. The mechanisms governing thermal and environmental degradation, as well as thermoelectric leg interface performance, are discussed alongside strategies for enhancing material stability and optimizing contact interfaces. Representative studies on stability enhancement are also reviewed. Finally, remaining challenges are identified, and future research priorities for developing stable and reliable N-type Mg₃Sb₂-based thermoelectric materials and devices are proposed.