The 1896-1901 Milanese period is a key one to understand Einstein’s training background. When he was a student at the ETH in Zürich (the Swiss Federal Polytechnic in Zürich) from 1896 to 1900, he would make regular trips back to Milan to stay with his family who was involved in the development of the electricity industry in northern Italy. Between 1899 and 1901, he would meet his faithful friend and collaborator, Michele Besso in Milan on a regular basis. Given their relationship, the 1899-1901 Milanese period therefore foreshadowed the Bern period. In order to specify the circumstances under which Einstein and Besso got the chance to meet, we will show that their respective families did have interconnected social networks, especially through the electricity sector and the polytechnic engineering Universities of Zürich and Milan. The branch of the Cantoni family, on Michele’s mother’s side, rather ignored by now, played a crucial role: with Vittorio Cantoni, a renowned electrical engineer who had not been previously identified as being Michele’s uncle, and Giuseppe Jung, professor at the Milan Politecnico. We will also show that when staying in Milan, Einstein, who lived in a well-knownMilanese palace in the heart of the city, worked in the nearby rich library of the Istituto Lombardo, Accademia di Scienze e Lettere in Brera. The linkage between the scientific observations which can be found in Einstein’s correspondence and this library collection sheds new light on his scientific work, in particular on his original thesis.