Phase-change processes, such as boiling and evaporation, generally represent very effective modes of heat transfer. However, the demands of modern thermal systems have required the development of methods to achieve still higher performance by use of enhanced heat transfer techniques. While heat fluxes above 108 W/m2 have been accommodated in carefully controlled situations, the fluid and convective conditions usually dictate maximum heat fluxes several orders of magnitude lower. Two major contemporary areas, enhanced surfaces for pool boiling and enhanced surfaces for forced convection vaporization, are discussed. They illustrate the opportunities and challenges of enhanced heat transfer technology.