The fluids dispersed with nanoparticles known as nanofluids are promising for heat transfer enhancement due to their high thermal conductivity. In the present study, a literature review of nanofluid thermal conductivity is performed. The possible mechanisms are presented for the high thermal conductivity of nanofluids. The effect of some parameters such as particle volume fraction, particle size, and temperature on thermal conductivity is presented. Theoretical models are explained, model predictions are compared with experimental data, and discrepancies are indicated.