Magnetic data from measurements at moderate to high magnetic fields in the temperature range 1.4° to 300°K, lattice constants, and preparative data are reported for the systems {Gd3}[ScxFe2−x](Fe3)O12, {Gd2Y}[ScxFe2−x](Fe3)O12, {Gd3−xCax}[Fe2] (Fe3−xSix)O12, {Gd3−xCax} Fe5−xGexO12, {Gd3}Fe5−xAlxO12, {Gd3}[MgxFe2−x] (Fe3−xSix)O12, and for the three garnets {Gd2Ca}[ZrFe](Fe3)O12, {Gd0.6Y2.4}[ScFe](Fe3)O12, and {GdCa2}[Zr2](Fe3)O12.The following model for the general features of the 0°K magnetic structures of the substituted gadolinium iron garnets is proposed. At 0°K, gadolinium iron garnet itself is an ideal Ne´el ferrimagnet. The moments of the octahedral Fe3+ions and of the dodecahedral Gd3+ions are strictly antiparallel to the moments of the tetrahedral Fe3+ions. Replacement of some of the octahedral Fe3+ions by nonmagnetic ions such as Sc3+ions as in {Gd3}[ScxFe2−x](Fe3)O12causes random canting of the tetrahedral Fe3+ions. Because the strong interactions of the Gd3+ion moments are with those of the tetrahedral Fe3+ion moments, this leads also to random canting of the Gd3+ion moments thereby reducing the contribution of the dodecahedral sublattice to the net spontaneous moment of the garnet. Replacement of the tetrahedral Fe3+by nonmagnetic ions as in {Gd3−xCax}[Fe2] (Fe3−xSix)O12causes random canting of the octahedral Fe3+ion moments, but this is not expected to affect the alignment of the Gd3+ion moments. Such substitution appears to have the effect of removing from contribution to the net moment, those Gd3+ions which are not linked through oxygen atoms to at least one tetrahedral Fe3+ion.A comparison of the results on the systems {Gd3}[ScxFe2−x](Fe3)O12and {Gd2Y}[ScxFe2−x](Fe3)O12indicates that at or very near 0°K, the interaction in the dodecahedral sublattice appears to have a ferromagnetic component. Also the garnet {GdCa2}[Zr2](Fe3)O12appears to be a weak ferromagnet.