The climate negotiations up to Copenhagen will need to elaborate on measurable, reportable and verifiable (MRV) mitigation commitments and actions as part of the future of the climate regime. The conceptual, political, scientific, financial and institutional principles for MRV are explored for (1) mitigation commitments in developed countries, (2) mitigation actions in developing countries, supported by (3) means of implementation. For developed countries, the procedures in Articles 5, 7, 8 and 18 of the Kyoto Protocol will be critical in order to ensure comparability of commitments, both in effort and compliance. Outcomes should be reportable and verifiable through Annex I national communications and in-depth review. Existing procedures could be enhanced and need to apply across Protocol and Convention. MRV mitigation actions by developing countries should result in measurable deviations beiow baseline. Inventories will be important to measure, and enhanced national communications for reporting. The challenge will be to make mitigation actions verifiable, and options include verification by domestic institutions working to internationally agreed guidelines. A critical distinction is to be made between unilateral mitigation actions and those with international support. MRV applies to the provision of the means of implementation, including technology and finance. Investment in technology can be measured, so that institutional arrangements for technology and finance should be aligned. Verification of funds raised at international level would be simpler than raising funds nationally.