Chapter 2 of this thesis presents an X-ray structure correlation and reactivity study of hypervalent iodine compounds designed to facilitate the search for more effective reagents for the electrophilic trifluoromethylation of hard nucleophiles. In the second part of this thesis (Chapter 3) two methods for the N-trifluoromethylation of organonitrogen compounds utilizing hypervalent iodine compounds are described. Firstly, in a Ritter-type reaction, N-(trifluoromethyl)imine derivatives were prepared via acid-catalyzed trifluoromethylation of nitriles in the presence of various azoles. Secondly, the efficient and mild direct N-trifluoromethylation of various electron-rich heterocycles such as pyrazoles, indazoles, triazoles, tetrazoles and to a certain extent benzimidazole is described. Both methods provide ready access to a wide variety of stable N-trifluoromethylated compounds; rare substances which are otherwise very difficult to obtain.