Diplomacy is essential to integrating climate change into foreign policy, and developing the conditions for securing an international climate agreement by 2015. This policy brief outlines the critical elements of effective climate diplomacy; and identifies approaches that countries, especially the least developed countries (LDCs), can consider to develop their own capacity for successful climate diplomacy. Stronger climate diplomacy can support a successful outcome at the UNFCCC negotiations by helping to establish climate change as a national strategic priority. To achieve this, national political leaders need to gather the necessary intelligence; make the case for climate change as a key cross-cutting foreign policy issue; lead a national consultative process involving all stakeholders; and mandate strong cross-government work on climate issues. There are a number of practical actions that countries can pursue to help focus diplomatic resources on climate issues and develop capacity in climate diplomacy; these include the development of a climate diplomacy action plan, and the appointment of a climate envoy. Diplomatic directives and investments are necessary to support the development of technical knowledge among diplomats as well as the diplomatic skills of climate specialists. With stronger climate diplomacy, states can engage with climate change more effectively both bilaterally and multilaterally, within and beyond the UNFCCC. This brief includes lessons from least developed and most climate-vulnerable nations, such as the Republic of the Marshall Islands, which are starting to develop experience with climate diplomacy.