‘Useful outsiders: building policy reform dossiers’ argues that outsiders to environmental policy making in a development context can have an important contributory role in policy reform. Outsiders are broadly defined and include academic scholars, activists, international centres, non-governmental organizations, charities, social movements and trade unions. The role that outsiders can play in policy reform includes the creation of new knowledge through research (often with the subjects of research taking a symmetrically co-productive role), communication of this knowledge to key actors in policy making, and also lobbying. Any involvement in environmental policy in a development context has long attracted well-earned criticism. Earlier anti-development and post-development critiques have tended to dismiss any involvement by outsiders as contaminating and harmful for the ‘target populations’ for which ‘development’ was intended. We argue that more nuanced recent debates from political ecology and anthropology may enable outsiders to navigate their way through the many dangers of active participation in the policy-making process (for example, incorporation by senior policy-making elites, serving dominant economic and political interests or failing to listen to voices marginalized on account of ethnicity, gender, age, wealth). Also, the burgeoning literature on the policy-making process is useful in suggesting strategies for promoting progressive environmental policy. The method outlined here to develop a progressive approach to environmental policy making is the ‘policy reform dossier’. The dossier is a cumulative and integrated data set; it has an explicit political purpose (for example environmental justice); it is reflexive, concerns multi-scale partnerships and aims for a symmetrical co-production of knowledge; it is a flexible tool that allows the user(s) to negotiate their own evolving goals; and a well-thought-through set of practices of confidentiality and stakeholder access. The dossier has a number of files on different aspects of the policy that are initially decided by the outsiders themselves and then adapted as the process evolves. In this chapter the following files are suggested: policy goals and related issues, technical and scientific debates, time-line of events, actors in the policy process, actors’ narratives and claims, strategies for policy reform, and explaining policy outcomes (evaluation and lessons learnt).