Recent development of organic scintillators is reviewed from the viewpoint of materials science. Design and crystal growth of organic crystalline scintillators, use of novel solvents and solutes in liquid scintillators, and development of plastic scintillators based on novel polymer hosts or novel fluorescent molecules are introduced. Additionally, development of loaded liquid or plastic scintillators is reviewed on the basis of two approaches of loading: molecules or nanoparticles. A disadvantage of organic scintillators has been their low scintillation light yields. Hence, materials design for improving scintillation light yields is introduced in detail with description on related excited state dynamics. Finally, future prospect for the improvement of scintillation light yield is briefly given.