When we accepted the kind invitation of Prof. Dr. F.K. SCHMIDT to write a monograph on abstract harmonie analysis for the Grundlehren der Mathematischen Wissenschaften series, we intended to write aH that we could find out about the subject in a text of about 600 printed pages. We intended that our book should be accessible to beginners, and we hoped to make it useful to specialists as weH. These aims proved to be mutuaHy inconsistent. Hence the present volume comprises only half of the projected work. It gives all of the structure of topologie al groups needed for harmonie analysis as it is known to us; it treats integration on locaHy compact groups in detail; it contains an introduction to the theory of group representations. In the second volume we will treat harmonie analysis on compact groups and locally compact Abelian groups, in considerable detail. The book is based on courses given by E. HEWlTT at the University of Washington and the University of Uppsala, although naturally the material of these courses has been enormously expanded to meet the needs of a formal monograph. Like the other treatments of harmonie analysis that have appeared since 1940, the book is a lineal descendant of A. WEIL'S fundamental treatise (WEIL r 4J) 1. The debt of all workers in the field to WEIL'S work is weH known and enormous.