These are the proceedings of the first COUNTER workshop "Mashing-up Culture: The Rise of User-generated Content", Uppsala University, May 13-14, 2009. COUNTER is a European research project exploring the consumption of counterfeit and pirated goods. Sampling, remixing, mash-ups and appropriation are part of the digital creative milieu of the twenty-first century. Sites such as YouTube and deviantART have offered new outlets for creativity and become hubs for innovative forms of collaboration, thus playing their part in challenging modernist notions of what it means to be a creator as well as a consumer. Drawing on this general background, the ten papers presented in these proceedings are examining areas such as: Sampling, mash-ups, and appropriation; Creativity and collaborative practices; Creative Industries and intellectual property; Copyright, Cultural Heritage and Cultural Policy; and Formal and informal regulations of intellectual property. The ten authors are all contributing to an international and interdisciplinary scientific discussion on the mash-up. Mash-ups and user-generated content are social and cultural phenomena which in these papers are put into various contexts, from legal ones, over technology, to the nation as a framework.