Chapter 5 discusses various areas of air transport security that involve the private sector. Corporations are normally employed because they are supposedly able to bring a higher degree of efficiency to various tasks than government agencies. The first dimensions that the chapter considers are security screening technologies and personnel. A close collaboration between private firms and public authorities has historically characterized the evolution of security screening technologies and apparels. The chapter also discusses the access control, identity management and airport perimeter security; activities that are deployed by private security contractors. Especially important, in this context, are the perimeter intrusion detection systems aimed at preventing the access of unauthorized personnel onto the airfield. The chapter then discusses the aircraft operator security technology. Finally, the intelligence dimension including interdiction and research to prevent security related episodes is considered.