The co-evolution of society and potentially disruptive technologies makes decision guidance on such technologies difficult. Four basic principles are proposed for such decision guidance. None of the currently available methods satisfies these principles, but some of them contain useful methodological elements that should be integrated in a more satisfactory methodology. The outlines of such a methodology, multiple expertise interaction, are proposed. It combines elements from several previous methodologies, including (1) interdisciplinary groups of experts that assess the potential internal development of a particular technology; (2) external scenarios describing how the surrounding world can develop in ways that are relevant for the technology in question; and (3) a participatory process of convergence seminars, which is tailored to ensure that several alternative future developments are taken seriously into account. In particular, we suggest further development of a bottom-up scenario methodology to capture the co-evolutionary character of socio-technical development paths.