The present volume, Organoiron Compounds B 16a, systematically covers the literature through mid 1990 and also includes many later references. This volume continues Series B (volumes B 1 to B 15 and B 17 already published) on the mononuclear organoiron compounds; Series A (volumes A 1 to A 9 already published) is devoted to the ferrocenes and Series C (volumes C 1 to C 5 and C 7 already published) treats organoiron compounds with two or more Fe atoms in the molecule. The present volume comprises compounds with one 5L ligand and one carbene ligand (including a single compound with two carbene ligands). Some di- or trinuclear carbene complexes are added for completeness. Most compounds contain the C5H5(CO)2Fe, the C5H5(CO)(2D)Fe, or similar groups, whose electronic structure causes the preferred species to be cationic. They are considered to be Fe-substituted classical carbenium ions as well as Fe=C species because of the -donor/+-acceptor properties of the ligands. Finally, cationic complexes with one 5L ligand and one vinylidene ligand are described. The volume is completed by an Empirical Formula Index and a Ligand Formula Index.