The author addresses the concept of social defences as originated by Isabel Menzies Lyth. After reviewing the origin and development of the concept, he discusses some of the challenges encountered in using it in the service of meaningful change, and finally highlights some features of emerging 21st century organizations that are well suited for social defence analysis. Social defences, in Menzies Lyth's sense, are aspects of organizations that: (1) exist independently of their members, such as structures and policies; and (2) come to serve the purpose of reinforcing peoples' defences against the primitive anxieties stimulated in the workplace. The concept illuminates otherwise hidden sources of resistance to change and, as such, provides a valuable perspective on the challenges of continuous change and adaptation required of contemporary organizations.