Understanding of oxorhenium(V) Rhenium(V) complexes as radiopharmaceuticals for therapy and diagnosis have received attention, because of their suitable radionuclear properties, i.e., 186Re: Emax = 1.1 MeV for beta-emission and Emax = 0.137 MeV for gamma-emission with t1/2 = 90.6 h, 188Re: Emax = 2.1 MeV for beta-emission and Emax = 0.155 MeV for gamma-emission with t1/2 = 17 h. Hence, chemical properties of various monooxo- and dioxorhenium(V) (ReO3+ and ReO2+) complexes have been examined as basic studies for their application to radiopharmaceutical. However, only limited information is available concerning the electrochemical properties and stereoisomerism of oxorhenium(V) complexes in non-aqueous solutions, in spite of importance in the relation to in vivo behavior, i.e., the reactivity towards redox agents. This book is covering a doctoral study and its results on the related subjects.