In this paper we report results on microstructural and compositional characterization of (Fe1-x-yCay)O, (Re1-x-yMny)O and (Fe1-x-yMgy)O wustites and their reduction behaviour using optical, scanning and transmission electron microscopy and X-ray microanalysis. The microstructure of mangano- and magnesio-wustites does not show any significant differences when compared to FeO. This is due to the complete solubility of Mn and Mg in FeO and to small differences in ionic sizes between iron and these elements. In contrast, due to significant differences between iron and calcium, the microstructure of calcio-wustite consists of stacking faults in an ordered matrix. The density of the stacking faults increases with respect to Ca addition, up to about 1.5 wt% of Ca. Further addition of Ca atoms results in the precipitation of CaFe5O7 calcium ferrite plates as a consequence of low Ca solubility in FeO and its segregation to the stacking faults.