A specialist in Islamic bibliographic studies, Dr Gacek studied Arabic philology at the Jagiellonian University of Krakow in Poland and Librarianship at the Polytechnic (now University) of North London. Subsequently he worked at the School of Oriental and African Studies, University of London, preparing a catalogue of Arabic manuscripts in its library (published in 1981). In the early 1980s he occupied the post of Librarian at The Institute of Ismaili Studies, and is at present Head of the Islamic Studies Library at McGill University, Montreal.