The present volume on organomolybdenum chemistry completes the description of the rich chemistry of the 15-electron fragment 5LMo(CO)2. The 5L ligands are ring systems and represent mainly C5H5, indenyl, and C5(CH3)5 or several other substituted derivatives of C5H5. The first sections describe the bonding of this fragment to other 1L systems which formally contribute one electron in the form of alkyl and aryl groups or various side-on bonded E=CR2 derivatives, two electrons in the form of carbene, isonitril, or ylide ligands, and even three electrons in the form of carbyne ligands, resulting in a formal molybdenum-to-carbon triple bond represented by the general formula 5LMo(CO)2hCR. Three other sections deal with the bonding of this fragment to 2L ligands (mainly olefines). 3L ligands (allyl, trimethylenemethane derivatives), and 4L ligands (derivatives of butadiene). Various neutral two-electron donors, halogens or other -bonded heteroatoms, and charges satisfy the electron requirement of the compounds in obeing the Effective Atomic Number rule. In compounds with four different types of ligands and with a cis arrangement of the two CO groups, metal chirality appears. These options generate versatile types of compounds and isomers, thus stimulating further research in this area. An empirical formula index and ligand index at the end facilitate the compound search.