In 1964 I was searching for a place to pursue a doctoral thesis. At that time I was carrying out my diploma thesis at the Technische Universität Hannover in the group of Walter Theilacker. I was working on the task of preparing the first long‐lived dialkylarylmethyl radical, in which I did not succeed. My bench neighbor Horst Böhm, a PhD student, was more successful. He was able to determine the very low rotational barrier of 2,2′‐dimethylbiphenyl, a difficult problem even today, by carrying out ingenious experiments that involved polarimetry at below −30 °C: E A =15.1±0.4 kcal mol−1. Horst took inspiration from Eliel's Stereochemistry of Carbon Compounds (1962), which was usually on his desk and often consulted. His enthusiasm was infectious, and I started also to study this book. It was full of references and had an index of names. Only four authors had four lines in the register: Eliel, Allinger, Djerassi, and Prelog. Horst told me that Prelog was considered the “pope of stereochemistry” and that the ETH Zürich was one of the world's top universities. I applied and was accepted to start work in 1965.

My new home was lab D110, the lab nearest to Prelog's office. My labmates were the habilitands Hans‐Herrmann Westen and Hans Gerlach, and slightly later the PhD student Georges Haas. I encountered a lab that was partially covered with sheets of paper, versions of the manuscript of the publication that eventually appeared in April 1966. Professor Prelog, “Pg” among co‐workers and addressed as “Vlado” by American postdocs, usually hurrying along in a white, unbuttoned lab coat, and often came in for last‐minute changes, which were accompanied by discussions and anecdotes, which Prelog loved to tell.

First Steps—London 1951 I learned that the system was initiated by Robert S. Cahn (London), the editor of the Journal of the Chemical Society, in order to cope with an increasing number of structures, the configuration of which could not be adequately described by the Fischer–Rosanoff d,l convention. He asked Christopher K. Ingold of University College London for help, and Ingold, an intellectual giant, came up with the rudiments, published by the two in 1951,1 of what later became the CIP system. However, they kept the descriptors d and l. Prelog came in not only because of his extensive research on various stereochemical issues, but also because he succeeded his teacher Emil Votoček (Prague) in the 1950s as member of the IUPAC Commission on the Nomenclature of Organic Chemistry. The collaboration began in 1954 at a conference in the Manchester area, which was concluded with a dance. Among the people who were not dancing, Prelog spotted Ingold and Cahn, whom he knew from the IUPAC commission. A lively discussion and criticism of their system closed with the invitation to join the team.

The R,S System—1956 The result appeared in the journal Experientia only two years later.2 In the meantime, Bijvoet (1951) had determined, for the first time, the absolute configuration of an organic compound. Furthermore, a variety of new description types were introduced, for example, pseudoasymmetric units, chirality axes, and chirality planes. All this required a fundamental distinction from the Fischer system, which was made visible by introducing the descriptors R and S. Adoption of the R,S system, as it was called before 1966 by the chemical community, was by no means guaranteed as other scientists developed rules for the same purpose. Here, membership of the aforementioned IUPAC commission was of great importance, because among its members were editors of important journals and handbooks, for example, Cahn, and Friedrich Richter, the Editor of the “Beilstein”, who adopted the R,S nomenclature and applied it to numerous examples. The Beilstein editors encountered a number of difficulties, which were regularly discussed with Prelog, who transferred the experience to Cahn and Ingold. Finally all this evolved into a new manuscript, to which Hans‐Herrmann Westen contributed considerably.

The CIP System—1966 The publication “Specification of Molecular Chirality”3 in Angewandte Chemie was an immediate and lasting success. The title was to change the everyday language of chemists by bringing the term chirality to their attention. This term had been created by Lord Kelvin in the 19th century and was “discovered” by Kurt Mislow. A former guest professor at the ETH and friend, he generously left it to Prelog to unveil it to the chemical community. The article was a comprehensive outline of the system with numerous examples and in‐depth explanations of problematic specifications, many of which had been brought forward by the Beilstein experts as well as chemists from all over the world. Most examples referred to molecules that had chiral centers with four ligands. An extension to coordination compounds with up to six ligands, mostly octahedral complexes, considerably widened the scope. The system was further extended to include conformations as well as helical stereomodels, which were specified with the new descriptors M (minus) and P (plus). It was clearly recognized that compounds with a chiral axis, for example, biaryls, can be specified either by using a model based on an elongated tetrahedron, descriptors aR and aS, or by the conformational approach, descriptors M and P. A similar treatment was already in use for the chirality plane. It was an unfortunate coincidence that aR corresponds to M in case of the axis. This is not known to many users and has caused numerous erroneous descriptions.