We adopt the broad conceptualisation of Green Information Communication Technology (ICT) used by the Organisation for Economic Cooperation and Development (OECD), incorporating perspectives on Information Technology (IT) and Information Systems (IS) which has currency with both business practitioners and policy makers. The objective of our research is to develop a theory of the institutional mechanisms that underpin socio-technical transitions to environmental sustainability through the direct, indirect and systematic effects of Green ICT in and across organisational fields. We construct our theory by drawing on published research in several disciplines focusing on the organisational field of the ICT industry. We present a mechanism-based theoretical model that explains how institutional change in organisational fields can evoke appropriate socio-technical transitions and organisational responses to Green ICT. Systems researchers agree that Green ICT can help lower GHG emissions directly, through energy efficiencies and indirectly by enabling environmentally sustainable business processes. If this research is to be of theoretical or practical relevance it must recognize that government organizations and business enterprises may not adopt policies and strategies on Green ICT because it is rational or moral to do so rather, a web of social, and institutional mechanisms interact to produce the outcomes observed in practice.