As a form of public engagement, science festivals have rapidly expanded in size and number over recent years. However, as with other domains of informal public engagement that are not linked to policy outcomes, existing research does not fully address science festivals’ impacts and popularity. This study adduces evidence from surveys and focus groups to elucidate the perspectives of visitors at a large UK science festival. Results show that visitors value the opportunities afforded by the science festival to interact with scientific researchers and to encounter different types of science engagement aimed at adults, children and families. The most significant self-reported impact of attending a science festival is the development of increased interest in and curiosity about new areas of scientific knowledge within a socially stimulating and enjoyable setting.