Betty de Hart focuses on European and national migration law, which comprises areas such as aliens law, nationality law and private international law. She conducts comparative, empirical and historical international research into each of these areas of law. She is especially interested in the legal regulation of transnational families. 

De Hart’s publications include the book Een tweede pas. Dubbele nationaliteit in de Verenigde Staten, Duitsland en Nederland (Amsterdam University Press, 2012). In 2007, she received a Vidi grant from the Netherlands Organisation for Scientific Research (NWO) for her research project ‘Transnational families between Dutch and Islamic family law’. In 2003, she defended her doctoral thesis Onbezonnen vrouwen. Gemengde relaties in het nationaliteitsrecht en het vreemdelingenrecht. 

De Hart has participated in various international research projects in areas such as dual nationality, family reunification and nationality law in the fifteen ´old´ EU member states. She is currently chronicling the life stories of Dutch women who married foreigners before 1964 and subsequently lost their Dutch nationality. 

De Hart has been affiliated with Radboud University Nijmegen since 2002, where she has served as Senior University Lecturer in Migration Law and Sociology of Law since 2008. De Hart is a member of the Advisory Board of the International Child Abduction Centre. She is also a member of the board of the Association for Socio-Legal Studies.