Heij did his phD research at the University of Groningen in the 1980s among other young system theorists, such as Hans Nieuwenhuis, Pieter Otter, Jan Camiel Willems, and Dirk T. Tempelaar [REF].
In the 1990s Heij continued his research at the Econometric Institute of the Erasmus University Rotterdam, and wrote a series of books on systems theory, modelling, dynamics systems, and econometrics.