This volume is the first of two volumes describing mononuclear cyclopentadienyl rhenium compounds. All chemical, physical, and catalytic properties are given. The major part is devoted to the class of (C5H5)Re compounds without CO groups. The most important species within this class are the NO and PR3 derivatives. Another section describes compounds containing one CO group and closes with 5LRe(CO)2 compounds without additional organic mL ligands (ligands bonded by m C atoms to rhenium). An important starting material for the preparation of other organorhenium compounds is ÄC5H5Re(CO)2NOÜ+. This compound, as well as many others, is of interest in comparison with the analogous organometallic compounds of Cr, Mo, W, and especially Mn. The empirical and ligand formula indices provide ready access to the desired compounds.