Abstract: We have examined the possibility to dope, in particular Cu2O, with a series of aliovalent and isovalent ions. Detailed measurements were done on Ag and Co doping. Other ions considered were: Li+, Na+, K+, Ni2+, Bi3+, and Wi+, (i=4 or 6). The solubilities found were low, usally below ~0.1%cation, except for Ag+ which dissolved with 2%cation. An analysis is presented that allows calculating the solubilty limits. The concepts of “corresponding native defects” of the host material is introduced. With a knowledge of the concentration of the “corresponding native defects”, the standard chemical potential of the materials involved and the shear modulus of the host material, one can calculate the solubilities of the impurities. Using the results of that analysis to fit the experimental data the shear modulus of Cu2O is determined to be 1.7?1011 N/m2 , a value obtained from consideration of the strain on a microscopic atomic scale.