The present volume is a continuation of Series B on the mononuclear organoiron compounds. It covers the literature completely to the end of 1979 and includes occa- sional references to the literature up to 1982. This volume begins the description of compounds with 5L ligands, i.e., ligands bonded to the iron atom by five carbon atoms. 5LFe compounds are numerous, particu- larly those where 5L is cyclopentadienyl. The stability of a 5LFe unit permits many different ligands at the other three coordination sites of the iron atom. Thus the present volume can only cover apart of the 5L compounds. Main sections of the volume deal with 5LFe compounds containing other ligands of the D and X type and 5LFe compounds with an additional' L ligand, which include compounds with 5LFe(CO) units (complete in this volume) and 5LFe(CO)2 units (to be continued in B 12). Series B so far comprises volumes B 1 to B 7, and a survey of this series has been given in the preface to B 7 (1981). The missing parts, B 8 to B 1 0, describe the remain- ing 4LFe compounds and will appear in the near future.