The objective of the current study is to perform a careful investigation of the (Fe) and (W) solvus and of the intermetallic compounds in the Fe-W system as it could have a significant impact on higher-order systems based on this binary system. Two key alloys, Fe-14 at. pct W and Fe-50 at. pct W, and a diffusion couple were synthesized based on the literature. They were studied by long time annealing experiments with a selected heat treatment route, X-Ray diffraction analysis, and electron microprobe analysis with a careful control of impurity levels of C, Si, and O. The two intermetallic phases mu-Fe7W6 and lambda-Fe2W are characterized and the composition range of the mu-Fe7W6 phase is specified. The phase previously reported as FeW is most probably a ternary carbide with low carbon content. An accurate determination of the solubility of W in alpha Fe and of Fe in alpha W is presented.