Opportunities exist to make revolutionary impacts on convective heat transfer designs for high temperature applications as the development of three-dimensional metal printing technologies continue to advance. Not only can complex heat exchange designs be further exploited because of manufacturability, but the development of these new designs can be done cheaper and faster. This chapter highlights the importance of understanding the additive manufacturing (AM) processes in light of how the AM processes impact heat transfer, particularly for millimeter-sized channels and thin fins, which are used in many convective cooling applications. In particular, the surface roughness inherent in the AM process is a key contributor to performance. Surface roughness is a strong function of the build parameters as well as the component build direction. In addition to proposing a new correlation for predicting friction factor and heat transfer of internal channels and thin fins made using AM, a range of channel shapes and novel geometries are highlighted. Finally, this review details how AM has been used to build functional heat exchangers along with the expected performance relative to conventional designs.