Nanofluids are a class of fluids that contain dispersed nanoparticles, offering unique properties and promising applications. This chapter explored different types of nanofluids and their synthesis methods, with the one-step method offering simplicity and efficiency, the two-step method providing precise control, the micro-emulsion method providing excellent stability, the sol-gel method providing well-defined nanoparticles, the chemical reduction method offering versatility, the laser ablation method offering high purity, the green synthesis method highlighting eco-friendliness, and the plasma-based method requiring sophisticated equipment.