Our recent studies on effective halogenation and oxidation using benzyltrimethylammonium polyhalides, stable solids, are described. Those involve electrophilic halogen-substitution (bromination, iodination, and chlorination) of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophenes, α-halogenation of arenes and acetophenones, and also halogen-addition of alkenes by the use of benzyltrimethylammonium tribromide (BTMA Br3), benzyltrimethylammonium dichloroiodate (BTMA ICl2), and benzyltrimethylammonium tetrachloroiodate (BTMA ICl4). Furthermore, oxidation of alcohols, ethers, 1, 4-benzenediols, hindered phenols, primary amines and hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are presented.