Abstract Background and Objectives Human research ethics statements support the equitable inclusion of diverse groups. Yet older people are underrepresented in clinical research, especially those with impaired decision-making capacity. The aim of this study was to identify the perspectives and experiences of older persons and their caregivers of research participation with impaired decision-making capacity. Research Design and Methods Scoping review of the literature and online sources in January–February 2019 (updated June 2020) according to Joanna Briggs Institute methodology and PRISMA Extension for Scoping Reviews. English-language peer-reviewed research articles and Australian online narratives were included. Data were tabulated and narratively synthesized. Results From 4,171 database records and 93 online resources, 22 articles (2000–2019, 82% United States, 16 first authors) and one YouTube webinar (2018) were initially included; updated searches yielded an additional article (2020) and YouTube webinar (2020). Studies were heterogeneous in terminology, methods, and foci, with hypothetical scenarios, quantitative analyses, and examination of proxy consent predominating. Participants (N = 7,331) were older persons (71%), caregivers of older persons with dementia/cognitive impairment (23%), and older persons with dementia/cognitive impairment (6%). Synthesis identified 2 themes: willingness to participate and decision-making approaches. Discussion and Implications Research participation by older persons with dementia may be optimized through reducing risks and burdens and increasing benefits for participants, greater consumer input into study development, and shared and supported decision-making. Older persons’ and caregivers’ perspectives and experiences of research participation with impaired decision-making capacity require investigation in a greater range of countries and conditions other than dementia, and dissemination through more varied media.