On the occasion of 125-year-anniversary of the German Federal Physical-Technical Institute (Physikalisch-Technische Bundesanstalt PTB), this book is dedicated specifically to the architectural history aspect of the long-standing Berlin-Charlottenburg establishment, which constitutes the birthplace and the scientific nucleus of the former Reich Institute and current Federal Institute. Up until now its multifaceted architectural history has in fact never been the focus of a comprehensive historical review. This is all the more surprising in light of the fact that the original buildings, along with the later plans and additions in the different styles of their time, are impressive reflections of the defining development stages of this historic scientific establishment.