Nanofluids are heterogeneous suspensions of nanoparticles in common fluids (base fluids) and have been the subject of investigation for numerous research projects since 1995. A great deal of experimental data indicates that the addition of very small quantities of nanoparticles to base fluids has the following effects on the heat transfer characteristics of the mixture: (1) Increases significantly the effective thermal conductivity of the suspensions; (2) Increases by a higher amount the convective heat and mass transfer coefficients; (3) In general, decreases the pool boiling and convective boiling coefficients; and (4) Significantly enhances the critical heat flux. Several early experiments showed convective heat transfer coefficient enhancements higher than 100%, but more recent experimental studies show enhancements closer to 50%. Typical critical heat flux enhancements are more than 100%. Such experimental observations indicate that, appropriately designed engineering systems operating with suitable nanofluids will have heat and mass transfer characteristics that are far superior to the heat transfer media that are currently used.