As part of the debate on the legitimacy of governance networks in global environmental politics, this article investigates the conditions under which policy solutions can be transferred worldwide as a result of a particular type of interaction within transnational expert networks and technical committees. To this end, the article hypothesises that policy solutions can be legitimised in governance networks meeting four cumulative criteria: participation, flexibility, horizontality and inclusiveness. This hypothesis is then tested by means of two heuristic case studies dedicated to the worldwide transfer of environmental standards via United Nations specialized agencies. The empirical work partly strengthens the validity of the hypothesis but also underscores the limits of legitimation strategies in the face of strong heterogeneity of interests. In such cases, environmental policy networks may adopt fairly “vertical” features and resort to classical bargaining and constraint strategies whereby compromises are exchanged and power asymmetries are mobilised.