Over the last decades, a shift towards participatory approaches could be observed in cultural heritage institutions. In co-curation processes, museums collaborate with public audiences to identify, select, prepare, and interpret cultural materials. This article focuses on the question how to engage and motivate local communities or individuals in rethinking dominant discourses or expert narratives regarding cultural heritage and bringing in their own experiences and knowledge. Based on four case studies of cultural co-curation, we delineate two basic challenges for this process: (1) Authority—even though museums strive to involve the public, there is still an imbalance in participation due to the museums’ authoritative status. (2) Motivation—participation in co-curation processes requires high levels of motivation, which are difficult to achieve. Based on the media synchronicity theory, we discuss which characteristics of new media technologies can be helpful to overcome these challenges. Media can increase awareness on counternarratives and blind spots in cultural collections. They can provide a setting where the participants can easily contribute, feel competent to do so, are empowered to rethink dominant discourses, develop a sense of relatedness with other contributors, and maintain autonomy in how and to which degree they engage in the discourse.