This review discusses the preparation, properties, stability, and thermal performance enhancement of nanofluids in heat transfer applications. Nanofluids, which are suspensions of nanoparticles in a base fluid, offer improved thermal conductivity and heat transfer efficiency compared to conventional fluids. Metallic oxides such as MgO, TiO₂, and ZnO are effective for enhancing thermal conductivity. The stability of nanofluids is crucial for their practical application, and various methods like surfactant addition, ultrasonic mixing, and pH control are used to enhance stability. The thermal performance of nanofluids is influenced by factors such as nanoparticle concentration, size, shape, and the base fluid's properties. The review highlights that increasing nanoparticle concentration can enhance heat transfer efficiency up to a certain point, but excessive concentration may reduce Brownian motion due to increased viscosity and density. The review also discusses the impact of nanoparticle size and shape on thermal conductivity, noting that smaller and specific-shaped nanoparticles can significantly improve thermal performance. Additionally, the effect of temperature on thermal conductivity is explored, showing that thermal conductivity increases with temperature. The review emphasizes the importance of balancing enhanced thermal performance with increased pressure drop and pumping power requirements. Various models and equations are presented to evaluate the thermal performance of nanofluids, including the effect of nanoparticle concentration, size, and shape on thermal conductivity and viscosity. The review concludes that nanofluids offer significant potential for improving heat transfer efficiency in various applications, but further research is needed to optimize their performance and stability.This review discusses the preparation, properties, stability, and thermal performance enhancement of nanofluids in heat transfer applications. Nanofluids, which are suspensions of nanoparticles in a base fluid, offer improved thermal conductivity and heat transfer efficiency compared to conventional fluids. Metallic oxides such as MgO, TiO₂, and ZnO are effective for enhancing thermal conductivity. The stability of nanofluids is crucial for their practical application, and various methods like surfactant addition, ultrasonic mixing, and pH control are used to enhance stability. The thermal performance of nanofluids is influenced by factors such as nanoparticle concentration, size, shape, and the base fluid's properties. The review highlights that increasing nanoparticle concentration can enhance heat transfer efficiency up to a certain point, but excessive concentration may reduce Brownian motion due to increased viscosity and density. The review also discusses the impact of nanoparticle size and shape on thermal conductivity, noting that smaller and specific-shaped nanoparticles can significantly improve thermal performance. Additionally, the effect of temperature on thermal conductivity is explored, showing that thermal conductivity increases with temperature. The review emphasizes the importance of balancing enhanced thermal performance with increased pressure drop and pumping power requirements. Various models and equations are presented to evaluate the thermal performance of nanofluids, including the effect of nanoparticle concentration, size, and shape on thermal conductivity and viscosity. The review concludes that nanofluids offer significant potential for improving heat transfer efficiency in various applications, but further research is needed to optimize their performance and stability.