In this book, The main objective of the work has been to study the influence of Ni-Cu/Ni-Mg co substitutions on various magnetic, electrical and structural properties of lithium ferrites. For this purpose, a systematic study has been carried out on mixed lithium ferrites with the chemical formulae Li0.5-x Nix Cux Fe2.5-xO4 (LNC) and Li0.5-x Nix Mgx Fe2.5-xO4 (LNM), where x varies from 0.00 to 0.25 in steps of 0.05. The selected compositions in powder form were synthesized by conventional ceramic process before compacting them into discs and toroids for sintering at 1000 oC for 6 hours. Characterization of the samples (both the powders and the compacts) was done by several techniques such as XRD, FTIR, SEM, VSM, Curie temperature etc. Structural, electrical and magnetic parameters like density, microstructure, dc resistivity, Curie temperature, dielectric constant, initial permeability and loss factor as a function of composition and/or frequency on the LNC and LNM ferrites are reported and discussed in this Book.