The aim of these two volumes is to provide an up-to-date text about the developments in the field during the last 5 - 10 years. Authors with an outstanding record both as active investigators and as critical reviewers have been selected. The result is an integrated collection of contributions forming a fundamental reference work for undergraduate and graduate students, and for those involved in research and teaching in biochemistry and related subjects. Part I contains 15 papers dealing with general aspects of hormones and their actions.