As long as there have been museum collections they have been interpreted and displayed according to the prevailing philosophy of their time. In the post-modern period many schools of thought have influenced museum interpretation, amongst them Constructivism. The model of the Constructivist Museum is one where visitors are involved in the process of interpretation and the construction of knowledge. Though examples of this have been rare in the world of physical museum display, with advances in technology and the development of the World Wide Web, visitors to online museums have more opportunity for participation. This paper examines how and if the concept of the Constructivist Museum is manifesting itself in the world of museums and the Web. Using several online projects as examples, it seeks to discover how user-generated content is being incorporated into museums and why there is a reticence amongst the public to dispute or edit official interpretation. It examines issues of trust, authority and the challenges to the traditional hierarchy of knowledge that arise in its doing so. This paper contends that whilst user-generated content is often encouraged on museum websites it is rarely allowed to infiltrate the official museum interpretative process and suggests that reluctance amongst museum professionals and curators to relinquish power and control might be responsible. It also suggests that museums might need to review the way they interact with their users in terms of presenting content on existing internet platforms.