This paper analyses ways to enhance the effectiveness and the contribution to sustainable development of the means that may be available to Annex I Parties to reach their emission reduction targets, as well as relevant methodological issues, including methodologies to be applied for estimating anthropogenic emissions and the global warming potentials of greenhouse gases. The options analysed have been identified on the basis of views of Parties, as contained in annexes II, IV, V and VII to the report of the resumed fifth session of the Ad Hoc Working Group on Further Commitments for Annex I Parties under the Kyoto Protocol. This paper describes each option and provides a brief analysis of the following aspects of each: rationale, key elements to be decided, necessary follow-up actions, potential challenges, implications for the emission budgets of Annex I Parties, possible impact on the carbon market, implications for domestic mitigation, links to other options, and ancillary benefits and costs.