The effects of alloy composition and reaction atmosphere on reaction synthesis of binary Fe-Al alloys were studied. Reactions were observed in an open (air) furnace, under static vacuum (in an evacuated quartz tube) and in a dynamic vacuum furnace. High-speed videotapes of reaction syntheses of compacts formed from 45-μm Fe and 10-μm Al powders reacted in air and under static vacuum revealed that an unusual “two-stage” reaction exists in this system under these conditions. The first stage of the two-stage reaction lasts several seconds and starts at around 650°C. The second stage begins at about 900°C, reaching temperatures between 1250 and 1350°C. The progress of the reaction to the second stage is sensitive to the alloy composition and reaction environment. The reaction behavior is explained in terms of thermodynamics and heat transfer, which control the delicate balance between heat accumulation and heat loss during reaction synthesis.