Ireland faces very challenging short-term targets in the period to 2020 arising from EU obligations that are specified in EU Directives and Decisions. In addition to these short-term targets, the EU has committed to a long-term greenhouse gas (GHG) emissions reduction of 80–95% below 1990 levels by 2050, and will require Member States to participate in effort-sharing to deliver deep emissions cuts. Policy-makers require comprehensive, robust, knowledge-based information to inform their decisions on how to meet these targets in a manner that will most benefit the Irish economy. This project draws on and contributes to the wealth of international energy-systems modelling research activity. It involved building, developing, calibrating, testing and running a (partial equilibrium) energysystems optimisation model for Ireland – the Irish TIMES model. The model was developed by University College Cork in collaboration with the Economic and Social Research Institute, E4SMA and KanORS over the period March 2009–November 2011. The real value of the Irish TIMES model is in the new insights it gives into some of the key challenges and decisions facing Ireland in energy and climate policy. The Irish TIMES model provides a means of assessing the implications of alternative future energy system pathways for: (i) the Irish economy (technology choices, prices, output, etc.), (ii) Ireland’s energy mix and energy dependence, and (iii) the environment. It is used in this project to assess the implications of emerging technologies and of mobilising alternative policy choices, such as meeting renewable energy targets and carbonmitigation strategies. The two key new perspectives this research project gives are: (i) a full energy-systems modelling approach and (ii) a focus on the medium term (to 2050) as well as the short term (to 2020). The scenario results respond directly to a number of key policy questions that could not be readily addressed before this model was developed. These relate to Ireland’s targets for: (i) renewable energy to 2020, (ii) GHG reduction to 2020 and (iii) long-term GHG emissions reduction to 2050. The results point to: 1 Alternative pathways for renewable energy to that currently being followed under Ireland’s National Renewable Energy Action Plan (NREAP); 2 The need to urgently reassess Ireland’s renewable energy policies in light of the non-ETS emissions reduction target; 3 A particular focus on renewable heat, renewable transport and electrification of heat, in contrast to the current dominant focus on wind-generated electricity; 4 The impacts of imposing a higher emissions reduction target on Ireland’s energy system to compensate for limited mitigation options in agriculture; 5 The significant challenges in moving to a lowcarbon economy in 2050 with renewable energy accounting for 65–85% of energy supply (compared with 6.5% in 2011); 6 Electrification of heat in particular but also of transport, resulting in the share of energy use delivered by electricity increasing from 18% currently to 31–47% of energy use in 2050.