[Chapter summary] Multinational corporations (MNCs) are major consumers of private security...Private security companies (PSCs) themselves are under increasing scrutiny in response to allegations that they have committed human rights abuses in conflict zones...MNCs using private security face numerous challenges related to their use of security...Weak oversight and regulation of private security forces create accountability gaps and potential conflicts of interest...This chapter focuses on some of the problems surrounding MNC use of private security and associated misuse of force or arms...It also reviews mechanisms that exist, both legal and otherwise, for holding MNCs accountable regarding their use of PSCs.