The tailoring of various garnet-type ceramic electrolytes for applications in energy conversion and storage was achieved in this thesis. For proton exchange membrane fuel cells, the garnet-type Li5+xBaxLa3-xNb2O12 (x = 0, 0.5, 1) was modified through a H+/Li+ ion-exchange reaction using water. The use of other exchange media including acetic and benzoic acid was also successful, as was the use of other garnet-type electrolytes such as Li5+xBaxLa3-xTa2O12 (x = 0, 0.5, 1). In all cases, the garnets with lower Li content showed a higher percent completion of the exchange reaction. The proton conduction in ion-exchanged Li5-yHyLa3Nb2O12 was also confirmed. For Li-ion batteries, the garnet-type Li5La3Nb2O12 was modified by doping with low levels of vanadium to increase density and Li ion conductivity. Various methods were employed to characterize the materials including powder X-ray diffraction (PXRD), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), 7Li nuclear magnetic resonance (Li-NMR), and AC electrochemical impedance.