Websites on Pestalozzi's Theory
https://www.heinrich-pestalozzi.de/
The most comprehensive online resource on Pestalozzi’s writings available in 9 different languages including Pestalozzi’s Letters on Early Education in the original German
A comprehensive presentation of Arthur Brühlmeier's excellent writing on Pestalozzi
http://www.centrepestalozzi.ch/accueil
Centre of Information and Research on Pestalozzi at Yverdon