This document, the executive summary of a book of the same title, synthesises an OECD project on the opportunities and trade-offs faced in mainstreaming responses to climate change in development planning and assistance. Country case studies review climate change impacts and vulnerabilities, analyse relevant national plans and aid portfolios and examine selected areas of natural resource management where climate change is closely intertwined with development. Findings are that:climate change is already affecting developmentfuture climate change impacts may also need consideration in development planninga significant portion of development assistance is directed at climate-sensitive activitiesdevelopment activities routinely overlook climate change and often even climate variability.There may also be barriers to mainstreaming climate change, for which there may be a number of complex reasons:segmentation and other barriers within governments and donor agencies limit mainstreaming: climate change expertise may be dislocated from development expertise, and donor agencies may have limited control over sectoral guidelines and projects. Managers may face "mainstreaming overload", and many development projects’ short funding cycles are not amenable to addressing long-term climate risksavailable climate information is often not directly relevant for development-related decisions: climate extremes are much more difficult to project than mean trends. Credible local-scale climate change projections are often lackingsometimes there are trade-offs between climate and development objectives: Governments and donors may have few incentives to divert scarce resources to investments that are perceived as not paying off until climate change impacts are fully realised. At the project level, mainstreaming can complicate operating procedures with additional requirements or considerations.Several opportunities exist for more effective integration of climate change considerations within development activities:making climate information more relevant and usable: provide credible and context specific information on the cost and effectiveness of integrating adaptation or mitigation measures within development planningdeveloping and applying climate risk screening tools: these are needed to assess the potential exposure of development activities to climate risks and to prioritise responsesidentifying and using appropriate entry points for climate information: includes land use planning, disaster response strategies and infrastructure design. Environmental Impact Assessments (EIAs) could be another entry point for mainstreaming both mitigation and adaptationshifting emphasis to implementation, as opposed to developing new plans: climate change only reinforces the need for iplementation of measures that already are environmental or development priorities. Putting the spotlight on implementation could put the focus on greater accountability in action on the groundencouraging meaningful co-ordination and the sharing of good practices: develop institutional mechanisms to forge links between mainstreaming initiated under the international climate change regime and the risk management activities of national and sectoral planners. Greater engagement of the private sector and local communities in mainstreaming efforts is also needed.