Immediately after the establishment of the NDH, all Jewish municipalities and organizations were closed. Several Jewish communities resumed their activities in May 1941, but under the supervision of the Ustasha political police. On 16 May 1941, the NDH Government established the Jewish Religious Community in Zagreb (ŽBOZ), an intermediatory for the implementation of anti-Jewish measures determined by the new state. Membership in ŽBOZ was mandatory for all persons defined as Jews according to the racial laws of the NDH. ŽBOZ organized several departments: municipal office, registry office, rabbinate, social welfare department, pharmacy, soup kitchen and improvised nursing homes in several apartments throughout the city. In addition, a Jewish preschool and school were established, as well as a residence for high school children, who were forbidden to attend regular high schools.
The financial means available to the community were always insufficient. The activities of ŽBOZ were financed by the membership fees of members who were rapidly impoverished due to the confiscation of property by trustees appointed by the NDH authorities. Additional sources were donations from Jews who fled to the territory under Italian control or to a neutral country, such as Switzerland, supporting their relatives imprisoned in NDH camps. Therefore, ŽBOZ depended on financial support and supplies from international humanitarian and Jewish organizations, especially the International Committee of the Red Cross (ICRC). ŽBOZ occasionally sent petitions to the Government to unfreeze the seized assets.
After the first mass arrests and deportations in 1941, ŽBOZ established the “Care for the Camps” within the Department of Social Welfare, which coordinated the procurement of food, medicine and other items and organized their delivery to various concentration camps. Jewish religious communities in Zagreb, Osijek and Sarajevo also supported Jewish detainees in camps in Loborgrad, Gornja Rijeka, Đakovo and Jasenovac and provided assistance to Jews detained in transit camps.
The key figures of ŽBOZ from 1941 until the last wave of deportations in May 1943 were President Hugo Kon (1871–1943) and Rabbi Miroslav Šalom Freiberger (1903–1943). They led the municipality and all activities, took care of all the Jews in the NDH and begged for help from various institutions and individuals in the NDH and abroad. They did this until they were arrested on May 3, 1943, and taken with their families to Auschwitz. Rabbi Freiberger refused the offer of Zagreb Archbishop Alojzije Stepinac to save him, deciding to share the fate of his community. A few days after the deportations in May 1943, Robert Glücksthal (1887–1972) and Oskar-Ašer Kišicky (1899–1979) assumed the co-presidencies of the Jewish Community. Both were protected through an “Aryan” spouse, although Asher Kišicki's wife converted to Judaism before marrying Kišicki. This is a good case study of the application of the racial definition of Jews in the NDH. ŽBOZ operated until the very end of the war, continuing, albeit on a much-reduced scale, to help the remaining surviving Jews in Zagreb and the camps on the territory of the NDH.