In the 16th and 17th centuries, Jewish converts to Catholicism and their descendants began arriving in Amsterdam from Spain and Portugal and, taking advantage of local religious tolerance, returned to the religion of their forefathers. To facilitate their rediscovery of the Jewish tradition, they opened Biblioteca Ets Haim, which has become the oldest Jewish library in continuous operation:
Ets Haim was founded in 1616 to help the newcomers start living publicly as Jews again. Many had continued to practice their true religion in secret while living outwardly as Christians. Amassing the library allowed them to debate among themselves, after so long, what being Jewish meant.
In 1675, the library moved to the Esnoga, the Portuguese Synagogue complex. . . . The library holds, in total, nearly 30,000 printed works dating back to 1484 and more than 500 manuscripts dating back to 1282. The documents not only represent centuries of Jewish thought and scholarship, but also the community’s everyday life. . . .
In 1889, David Montezinos, the librarian at the time, donated his substantial private library (20,000 books, pamphlets, manuscripts, and illustrations) to Ets Haim after his wife died.
Read more on Atlas Obscura: http://www.atlasobscura.com/places/biblioteca-ets-haim