Born in 1949, I attended highschool in Amsterdam (Waterlant-College) before enrolling, in 1966, at Free University (Amsterdam) as a student of chemistry and history of science. In 1976 I passed the "doctoraalexamen" (MSc) in both fields and turned to the history of science for a PhD, since 1980, under the aegis of the Centre Alexandre Koyré of the École des Hautes Études en Sciences Sociales of Paris. In December 1983 I passed the PhD under René Taton as formal 'directeur de thèse' (with Reijer Hooykaas), thanks to a research grant of the French Government. The dissertation covered the history of the concept of molecule until ca. 1800. A project aiming at a monograph covering that history until ca. 1925 was accepted in 1988 by the Royal Netherlands Academy of Sciences. As a research fellow of the Academy, then, I entered in the service of the University of Groningen. The first two years were spent in Paris to study source materials (Académie des Sciences, Bibliothèque nationale de France, Sorbonne, Arsénal, Muséum national d'Histoire naturelle, École des Mines, École de Pharmacie, École Polytechnique). The project culminated in 1996 in a 'habilitation à diriger des recherches', again at the École des Hautes Études en Sciences Sociales. The dissertation in question was subsequently completed and, in 2001, published in three volumes by Springer-Verlag France (Paris). In 2003-2005 an abridged and adapted Dutch edition came from the press of Verloren Publishers, Hilversum (NL). A globally meant English edition was published, in two volumes, in 2009 by Groningen University Press. It was realized through grants in aid of the Center for History of Physics of the American Institute of Physics (College Park, MD), the Chemical Heritage Foundation (Philadelphia, PA), and the European Physical Society. In 2006 the History of Physics Group of the European Physical Society elected me among its members. In 2012 I became 'corresponding member' of the International Academy of History of Science. Since 2009 a project runs aiming at the *Collected Papers of Frits Zernike (1888-1966)* and of a *Biography* of Groningen's first Nobel laureate (Physics, 1953). The first two volumes of Zernike's *Collected Papers*, featuring the original texts (FR, GE, DU) were published in 2012 by Groningen University Press. Volumes III and IV, with English translations of all papers, followed in 2016. To celebrate in a way the 15th anniversary of the Springer-Verlag France edition, the book *Making molecularism. I. Selected papers. I. Bibliography* was issued in 2016, again by Groningen University Press. In 2017 followed *Making molecularism II. Selected papers II. Abstracts* and in 2018 *Making molecularism III. Catalogus librorum &c. Selected papers III*. The series may be considered as the 'mémoires' of a retired historian: the successive volumes provide the background info indispensable for a correct understanding of the monographs that appeared before (and their forthcoming German version). They feature also something entirely new, namely the details of the calculation which led Max Planck in 1899-1900 to the constant that came to be called after him. This 'calculatio crucis' reveals at once Planck's inspiration: the thoroughly molecular kinetic theory of the 19th century. The new results also point to the necessity of a fundamental revision of the interpretation of Albert Einstein's pre-relativity papers, as promulgated by the editors of Einstein's *Collected Papers*, most notably by Anne Kox.
