Increasingly, museums and galleries are being asked by funders to reach new audiences as a condition of receiving money. This poses a problem to the sector: existing audiences are easy to reach; new audiences are much harder to get to, and are often resistant to traditional approaches. This paper shows how new technology can be used as a way not only of opening up collections to new audiences but also of engaging audiences on a deeper level than ever before through participation. Drawing on the experience and lessons learned from a raft of interactive projects, this paper looks at how to understand and define audiences, how to design virtuous circles of content that encourage and promote participation, and how to team up with the right organisations to reach target audiences.