Experimental phase diagrams for each transition metal (TM) doped ZnO nanoparticles have been established that explore the relation between growth parameters and single/multiple phases of Zn1-xTMxO. Study of magnetic properties of Zn1-xTMxO nanoparticles have been depicted for TM = Co, Mn, Fe. Technologically relevant “Room temperature ferromagnetism” was achieved in Fe doped ZnO nanoparticles and has been probed by various experimental techniques. Study on co - doped i,e., (Co, Mn and Fe) doped ZnO nanoparticles has also been presented. ZnMnO epitaxial thin flims grown on single crystalline sapphire substrate using PLD technique has been incorporated. Finite-size effect is well known to play central role in physics that differentiates nanometric system from their bulk counterpart. We have presented our investigation on the effect of nanometric grain size on electronic-transport, magneto-resistance and magnetic properties of prototype structurally characterized La0.7B0.3MnO3 (B = Sr and Ca) nano-dimensional CMR manganites, having grain size 14 to 36 nm. A phenomenological model has been proposed to analyze certain aspects of physical properties of nanometric manganites.