The initial gaps between economics-oriented top-down models of the costs of emission reduction and technology-oriented bottom-up models have largely disappeared. The energy efficiency paradox - the hypothesis that it would be possible to abate greenhouse gas emissions and save money - is now partly explained and partly further investigated with the appropriate economic and behavioural research tools. New hybrid models include enough technological detail and are therefore quite realistic. Current research focuses on technological development. One strain of analysis relies on highly aggregate and stylized economic methods, while another on highly disaggregated detailed engineering methods. Both approaches need to pay more attention to distribution and welfare issues and to policy instruments, and need to be better embedded in their context and in empirical research.