Whom do we trust? An ‘expert’, by standard definition, has particular skills or knowledge of their field. Today, a wide range of scientists, scholars, doctors, oracles, pundits and others are called upon to explain, judge, predict and guide decisions in diverse fields. What skills, knowledge, qualifications, or experience are included or excluded in expectations, assumptions and implementation of expertise? Seminars in this series will explore how experts, expert knowledge, and expertise come to be recognised as credible, legitimate, and authoritative, for example in relation to ‘lay knowledge’, or ignorance. Sites at which these ecologies may be explored include interfaces among experts themselves, as well as interactions with tools and models, and with decision makers and publics.