Magnetism of matters has two basic ingredients. While exchange and correlation are responsible to the stability of magnetic moment, magnetic ordering is controlled by orbital hybridization, which depends on the atomic arrangement and the mode of orbital occupation. Transition-metal oxides serve as an important playground where unique properties and phenomena can be observed as results of close correlation among magnetism, orbital ordering and lattice distortion. Fundamental aspects of their close correlation are discussed by taking some typical examples: LaMnO3, Ca2-xSrxRuO4 and Sr2FeMO6 (M = Mo, W and Re). (C) 2006 Elsevier Ltd. All rights reserved.