Demand for flexibility in electricity systems and the transition to the Smart Grid is increasing opportunities for demand response (DR). However, there are many barriers which prevent the full potential of DR being realised. Unlocking of this potential, through identification of DR enablers, can be aided through systematic classification and analysis of DR barriers. To this end, while previous works mostly focused on individual aspects, this paper develops a comprehensive ‘socio-techno-economic’ review, classification and analysis of DR barriers and enablers in a Smart Grid context. This provides an intellectual framework which may be used to underpin further work on the study and integration of DR. DR barriers are classified as either fundamental (i.e., relating to intrinsic human nature/essential enabling technology) or secondary (i.e., relating to anthropogenic institutions/or system feedbacks). Fundamental barriers are defined as economic, social or technological, whilst secondary barriers relate to political regulatory aspects, design of markets, physical (electrical network) issues, or to general understanding of DR. Subsequently, associated enablers for the defined barriers are suggested. Consideration of technical and commercial/social aspects for both power system and information and communication technology (the “internet of things”) domains provides a foundational contribution to improve understanding of DR within the Smart Grid paradigm. Finally, the complexity resulting from connections between various barriers, enablers and the energy system generally, and the existence of the signature characteristics of complex systems is acknowledged and implications discussed.