The motivation to expand PrivateMilitary.org and include a segment focusing on Adverse Private Forces (APFs) has it origins on a key argument put forward in the book Private Armed Forces and Global Security. The author of the book argues that a dichotomy in the private realm has emerged, whereby PMCs/PSCs legitimately work alongside state forces and multilateral actors deterring or counteracting the predatory advances of APFs. The author further suggests that the emerging and defining conflicts of the 21st century are likely to feature PMCs/PSCs (in partnership with state and multilateral forces) fighting against varied arrays of APFs. The main categories of APFs examined in the book and covered here are terrorist organizations, rebels and insurgents, pirates, mafias, and drug trafficking organizations. Thus, we hope this new segment will become a relevant resource to understand 21st century conflicts.