In a cyber defense competition, students design, configure, and maintain a set of servers and a network in a secure manner. The students’ goal during the competition is to prevent security breaches and to remediate any exploits that occur while maintaining a fully functional network for their end users. Cyber defense competitions provide active student learning, mimic real-world situations, and provide engagement with computer and network security topics. To date, Iowa State University has hosted 18 cyber defense competitions across four divisions: high school students, community college students, ISU students, and four-year university students from across the nation. This chapter provides a brief history of cyber defense competitions, as well as describes how they are run. The authors also address the needs of different audiences who participate in cyber defense competitions and show that beyond building and strengthening computer and network security skills, cyber defense competitions can be used for recruitment, retention, advanced training, and experimentation for students.