As the atrocities of World War II came to light, particularly the horrors of the Holocaust, the world's attention was initially drawn to the immense human toll and the quest for justice. Efforts were made to provide reparations and restitution, aiming to address not only the immense suffering but also the confiscation of property by the Nazis.

While the theft of valuable artworks, some worth millions, from Jewish families has been widely publicized, the story of the millions of Jewish-owned books plundered by Hitler's forces is less well-known. In their campaign to eradicate Jews and their culture, the Nazis looted books from European libraries, universities, and various public and private collections. Some were destroyed or sent to paper mills, but many were preserved for institutions the Nazis intended for so-called scholars to "scientifically" establish the Jews' inferiority. Although these institutions were never realized, the crates of stolen books were sent to sorting centers, often processed by forced Jewish labor.

Diane Mizrachi, a librarian at UCLA, was largely unaware of the story of the looted books until 2020 when she received an unexpected email. The message was from a curator at the Jewish Museum in Prague (JMP), who had been working to restore the collection of the Czech capital's Jewish Religious Community Library (JRCLP), which had been devastated by the Nazis. His meticulous search through an online repository of millions of digitized books led him to believe that several books at UCLA had once belonged to the library. Mizrachi recounted, "I received an email stating, 'I have discovered that three books in your collection bear the markings of the pre-WWII Jewish religious community library, and we would be interested in their return.' Unsure of how to proceed, I escalated the matter to higher authorities."

She later discovered that a similar request had been received from a German researcher a few years prior, and UCLA had "quietly returned the book." Mizrachi spent several months collaborating with the museum to investigate the origins of the three late-19th-century books in UCLA's possession. Eventually, six titles, including religious texts and rabbinical commentaries, were repatriated in a ceremony held in May 2022. "At UCLA, we possess dozens of such books, and I am certain that there are many more that remain unidentified. I am also engaging in partnerships with other librarians across North America, Europe, and Israel who are confronting their own looted Nazi-era books," Mizrachi stated. "I view this as a moral and ethical imperative. Whenever something is stolen, be it through imperialism, colonialism, or oppressive forces, it is a wrongdoing. It is a criminal act. The original owners might no longer be present, or even their descendants to whom we could return them, but their narratives are significant, and that is what we aspire to preserve."

Post-war, the remnants of the JRCLP were integrated into the Jewish Museum in Prague, yet with approximately 30,000 volumes and manuscripts plundered by the Nazis, many thousands are still unaccounted for. Michal Bušek, head of the museum's library department, revealed that the internet, digitization of books, online auctions, and the increase in provenance research have all bolstered the search efforts.

Approximately 2,800 titles are still missing from Prague, he mentioned in an email. These books are not only found on the shelves of university libraries but also concealed in museums, secondhand bookstores, and private collections, and listed in online auctions. Consequently, the process of recovering them is complex. The most favorable scenario, as exemplified by UCLA, is that the museum collaborates with the current owner to verify the provenance and, ideally, arrange for their return. Bušek's team has traced around 80 of the missing books so far and has managed to retrieve 63. He disclosed that the museum is currently in "negotiations" for the other volumes they have identified. The quest for Prague's missing books commenced during World War II when members of the city's then Jewish community endeavored to locate some of them, Bušek stated. "We continue the endeavors of our predecessors, who, despite their own lives being at risk, sought to preserve the heritage and testimony of the Jewish presence in Bohemia and Moravia (Czech provinces occupied by the Nazis). This Library or the books are all that remain of them. Their legacy endures. We aspire to bring the books back to where they rightfully belong."

In neighboring Germany, meanwhile, organizers of a pioneering exhibition are hoping it will inspire "citizen scientists – school children, students, historians, or anyone interested" to assist in tracing another group of plundered books. "The Library of Lost Books," which is both online and running in physical form at the University Library Frankfurt until January 31, focuses on the Higher Institute for Jewish Studies in Berlin (Hochschule für die Wissenschaft des Judentums), established in 1872 and dedicated to Jewish history, culture, and rabbinical studies. The institute was forcibly closed in 1942 under the Nazis, with some of its estimated 60,000 books destroyed and others boxed up and dispatched across Europe. The new exhibition features some of the looted books.

Unlike Prague's Jewish Museum, the "Library of Lost Books" is not seeking the return of the Hochschule books but aims to create a database of their locations. "As there is no legal successor, this is not a question of where these books belong," said Irene Aue-Ben-David, director of the Leo Baeck Institute (LBI) in Jerusalem, which has created the exhibition with its sister organization in the United Kingdom and the Association of the Friends of the LBI in Berlin. "For us, it is crucial that people are aware of the history of these books and report them so that we can document them online, but this is not about legal claims." The goal of the interactive project, according to organizers, is to enable ordinary people to "contribute to solving a mystery that has thus far remained unsolved" while achieving "a sense of justice in the face of a Nazi atrocity."