To achieve compact heat exchangers the surface geometries have to have high heat transfer surface area per unit volume. The flow passages then become narraow and the shape of the passages is often very complex. In addition, turbulators and surface modifications are used to enhance the heat transfer performance. During recent years, numerical methods for solving flow and heat transfer problems have been developed to such an extent that reliable predictions of the velocity and temperature fields, associated pressure drops and heat fluxes relevant to compact heat exchangers are possible in many cases. This work aims to show recent advances in computer simulations in compact heat exchangers as well as limitations and needs for further research and development.