Nees Jan is a senior researcher in the fields of bibliometrics and scientometrics working at the Centre for Science and Technology Studies (CWTS) of Leiden University. He has a PhD on the topic of visualizing bibliometric data. Together with his colleague Ludo Waltman, Nees Jan has developed VOSviewer and CitNetExplorer, two popular software tools for bibliometric visualization. The VOSviewer software is frequently used in bibliometric studies. More than 350 publications have appeared in international scientific journals in which the software is employed. Nees Jan has published more than 50 publications, mainly in bibliometric and scientometric journals but also in the fields of computer science, economics, and physics. He is editor brief communications of the Journal of the Association for Information Science and Technology and he serves in the editorial boards of Journal of Data and Information Science, Journal of Informetrics, and Scientometrics. Nees Jan has been involved in various commercial bibliometric research projects and training courses in which the VOSviewer software plays a key role. He is also the head of ICT of CWTS, making him responsible for the entire data infrastructure of the center.