This issue of the Johns Hopkins APL Technical Digest continues the presentation of articles that describe APL's approach to systems engineering that began in APL Applied Systems Engineering – Part I (volume 29, issue 4). Although the diversity of systems applications was clear in the first systems engineering issue, this diversity becomes even more evident in this second issue as we explore more complex issues in air defense, command and control, network communications, counter-improvised explosive devices, human-systems engineering, and nanosystems. APL's strong systems engineering culture and standard processes ensure that its products are fit for use regardless of the scope and complexity of the domain.