Mainstreaming has been adopted internationally as a key approach to promoting environmental concerns and opportunities in national plans and strategies, as well as in sectoral policies and plans. As the climate change response begins to look to mainstreaming as a way forward for adaptation, lessons should be learnt from the environmental mainstreaming experience on the forms of organisational arrangements adopted. From an analysis of experience in a range of southern countries, the article uses a framework of vertical and horizontal organisational arrangements for policy integration to assess which organisational forms have been adopted and with what implications. The review found a mix of experience, with strong political commitment seeming to support a vertical approach to organisational integration, with a lead, overarching agency, as opposed to a more horizontal approach with the ministry responsible for the environment leading. The theory and analysis suggests that a more promising approach to facilitate effective mainstreaming might be to combine elements of vertical and horizontal arrangements, at least over the medium term, where there is strong central commitment and capacity for sustained implementation. Copyright © 2012 John Wiley & Sons, Ltd.