Eutectic AuSn solder is increasingly used in high reliability and/or high temperature applications where conventional SnPb and Pb-free solders exhibit insufficient strength, creep resistance, and other issues. These applications include hybrid microelectronics (particularly flip chips), MEMS, optical switches, LEDs, laser diodes, RF devices, and hermetic packaging for commercial, industrial, military, and telecommunications applications. For most of these applications, AuSn provides the additional benefit of not requiring flux during reflow, significantly reducing the potential for contamination and pad corrosion. However, the materials and processing considerations are substantially different than for conventional solders. Many companies struggle with issues such as poor solder flow, excessive void formation, variable reflow temperature (arising from off-eutectic compositions), heterogeneous phase distribution, and others, all contributing to development delays, process yield loss, and field reliability issues. This paper reviews the critical issues in material and process selection, as well as long term diffusion and mechanical stability.