In chemical species containing of oxygen-halogens and nitrogen-halogens bonds, the halogen substituents show versatile reactivities, because oxygen and nitrogen atoms have higher electronegativity than halogen elements except for fluorine. I have focused on such monovalent halogen species and developed various synthetic methods utilizing O-X and N-X bonds which involves ionic and radical reactions. In this account, I describe such practical synthetic methodologies, which are CO2 fixation to unsaturated alcohols and amines, oxidative homo- and cross-coupling reactions of aromatic amines, novel generation of nitrile oxides from aldoximes, synthesis of oxazole-fused C60, iodoamination of alkenes in water, diaziridination of secondary amines, diastereodivergent diamination of unactivated alkenes, practical aziridination of electron-deficient alkenes, selective synthesis of nitrogen-bridged fullerenes, and benzylic C-H amidation.