This chapter was a brief introduction to the ever-evolving and complex area of network security. We discussed how to improve network security on Solaris 8 systems connected to TCP/IP networks (including the Internet). We also took a look at one of the free open source firewalls and two network intrusion detection systems available on Solaris 8. Basic network troubleshooting was also introduced, using Solaris’ own snoop and the open source tcpdump. Notwithstanding the number and quality of network security tools available today, network troubleshooting remains an area where knowledge and experience are the most important assets.