This report reflects on existing citizen research activity in the UK heritage sector by summarising both published research and current citizen research activity at Independent Research Organisations (IROs) and other heritage organisations, addressing the following questions: How do institutions and volunteers experience online citizen research; what are the motivations and rewards? Were projects successful in what they set out to do? What challenges have projects faced? What recommendations can be made based on the experiences of these projects? In December 2020, we circulated a call for information from cultural heritage practitioners in the UK running citizen research projects online. This report draws on the responses generously sent in answer to our call, focusing primarily on online projects based in the UK. A full list of the featured projects can be found in the Appendix. In July 2021, members of the Engaging Crowds project team coordinated a workshop at the Discovering Collections, Discovering Communities (DCDC) conference to gather insights from practitioners and researchers with experience of enabling and supporting online volunteering. The discussions from this workshop are also summarised in this report. A broad range of experience of citizen research in the UK is included in this report, from small-scale short-term projects, such as those set up to move pre-established volunteering projects online in response to the onset of the Covid-19 pandemic, to large-scale long-term citizen research projects. What is evident from all responses received to the call for information is that online citizen research projects bring many benefits to both volunteers and organisations, and also present a number of challenges. Successes relate to volunteer recruitment and engagement, as well as opportunities for increased data production and data quality. Data quality, however, was also reported by a number of respondents as an area of challenge, together with issues relating to chosen citizen research platforms and open access. In synthesising the experiences reported by responding projects and workshop participants, this report has identified a number of recommendations for future citizen research projects.