The present volume continues the series on "Organotin Compounds" which first appeared in 1975 and now comprises a collection of fifteen volumes. The overallplan of the series has been given in the preface of Volume 1. The present Volume 15 continues the description of the mononuclear organotin compounds with tin-oxygen bonds (Chapter 1.4.1 ). Treatment of organotin compounds with tin-sulfur, -selenium, and -tellurium bonds appeared earlier in 9, 1982, and 10, 1983. Chapters 1.4.2 to 1.4.4 of Volumes Volume 15 contains RSn-oxygen compounds with R = butyl, iso-butyl, sec-butyl, and 2 tert-butyl, covering the Literature completely to the end of 1985. Additional volumes describing tin-oxygen compounds with other RSn and RSn groups will follow in the near future. 2 Abbreviations and symbols are explained on pp. X/XI along with other remarks. We thank Prof. Dr. Dr. h. c. Ekkehard Fluck and his coworkers at the Gmelin Institute for their excellent cooperation. ln particular, we thank Dr. Ulrich Krüerke for his accurate and sympathetic editing, Mr. Edgar Rudolph for preparing the index, Dr. Grant for reading the drawing the numerous formulas and molec­ English text, and Mr. Hans-Georg Karrenberg for ular structures. We thank Mrs. Ellen Redlinger, Miss Susanne Schumann, and Miss Stefanie Schumann for their meticulous handling of the Literature index and the members of the chemical department of the Library at the Technische Universität Berlin for their assistance in searching and acquiring the references from the Literature.