Sonja Kruisinga is professor in Contract law at the Open Universiteit. She specialized in contract law. She has a special interest in European and international aspects of contract law. She is a specialist in international trade law, in particular on the 1980 UN Convention on Contracts for the International Sale of Goods (CISG). 

Next to her job at the Open Universiteit (OU) (and as honorary lecturer at Utrecht University), she is Professional Support Lawyer at Van Benthem & Keulen and deputy justice at the Court of Appeal in The Hague.