A Professor of demography at The Hebrew University's Avraham Harman Institute of Contemporary Jewry, and Institute Chairman until 2002, he is an internationally known specialist on Jewish populations and communities in Europe, North and Latin America and Israel. He has worked on Jewish historical demography, the Jewish family, Jewish migration and absorption in Israel and the Western countries, quantitative aspects of Jewish education, and population projections of the Diaspora, Israel and Palestine and Jerusalem. On these topics he has published numerous books and monographs and over 100 papers. In 1999 he won the \marshall Sklare Award for distinguished achievement from the Association for the Social Scientific Study of Jewry.