In the extensive literature on international environmental co-operation, trust is usually treated in terms of compliance and verification mechanisms, on the assumption that there will always be incentives for parties to international agreements to cheat or to 'free ride'. Indeed the establishment of adequate assurances that such behaviour will be detected and punished is frequently the sine qua non of agreement in the first place. Technical and legal compliance mechanisms have developed rapidly in environmental treaty-making over the last two decades. The climate regime is no exception and its provisions in this regard are briefly described and analysed. However, it will be argued that the development of trust amongst the parties goes well beyond formal compliance and depends upon the institutionalised relationships, often amongst officials and technical experts that have grown up, since the negotiations for a climate treaty commenced in the late 1980s. (C) 2009 Elsevier Ltd. All rights reserved.