My current research focuses on an understanding of electronic structures and magnetic properties of molecule based magnetic materials. On the basis of the electronic structures we are developing the theory of molecular design of molecule-based high-spin systems. Molecular systems applied are a wide range from organic high-spin systems to inorganic polynuclear complexes. The organic systems include polyradicals, poly-carbenes and nitrenes, and the polyionic states of the organic molecules. All compounds possess a high-spin ground or thermally accessible excited states. The inorganic systems include not only magnetically coupled transition metal systems but also rare earth metals. One of the rare earth metal systems is a europium(II)-doped aluminate which is a long-persistent phosphor. The aluminate is free of hazardous and radioactive substances, and has been attracting interest because of its potential for broad application.