Jan Just Keijser is an open source professional from Utrecht, the Netherlands. He has a wide range of experience in IT, ranging from providing user support, system administration, and systems programming to network programming. He has worked for various IT companies since 1989. He was an active USENET contributor in the early 1990s and has been working mainly on Unix/Linux platforms since 1995. Currently, he is employed as a senior scientific programmer in Amsterdam, the Netherlands, at Nikhef, the institute for subatomic physics from the Dutch Foundation for Fundamental Research on Matter (FOM). He works on multi-core and many-core computing systems and grid computing as well as smartcard applications. His open source interests include all types of virtual private networking, including IPSec, PPTP, and, of course, OpenVPN. In 2004, he discovered OpenVPN and has been using it ever since. His first book was OpenVPN 2 Cookbook by Packt Publishing in 2011, followed by Mastering OpenVPN, also by Packt Publishing, in 2015.