Objective: The objective of this scoping review was to identify and map the breadth of available evidence on relatives’ wants and needs for involvement in the care of patients with an acquired brain injury. Introduction: Acquired brain injuries often occur suddenly and unexpectedly. Experiencing an acquired brain injury has major consequences, not only for the patients—due to the devastating impact on their physical, cognitive, social, and psychological well-being—but also for the relatives who may need to take on a lifelong role as a carer. Research has cited some benefits of involving relatives in the care of patients, including positive effects on the patients’ health outcomes; however, there are few studies showing how relatives can be involved. Inclusion criteria: Studies that defined or assessed relatives’ wants and needs for involvement in the care of patients with an acquired brain injury in all settings were included. Studies were included if they described any kind of wants and needs for involvement experienced from the perspective of relatives. The review considered all study designs, except for literature reviews. Methods: The JBI methodology for conducting a scoping review was employed in accordance with an a priori published protocol. An extensive search was conducted in MEDLINE (PubMed), CINAHL (EBSCO), and Embase (Ovid). Gray literature was searched using Grey Matters and BASE. The initial search was conducted in February 2020 and updated in September 2021. This review was limited to studies published in English, German, or Scandinavian languages since January 2010. The data were extracted using a data extraction tool (authors, year of publication, country of origin, setting, study methods, and findings related to wants and needs for involvement) created by the authors. The review findings are reported as a descriptive summary, with tables and figures supporting the data. Results: The search identified 3854 studies, 31 of which were included. The studies were published between 2010 and 2021, and were conducted across 9 countries. In total, 16 studies applied a qualitative study design, 4 studies used a descriptive approach, 4 studies used a quantitative research design, 4 studies reported using a mixed methods design, and 3 studies employed a multi-methods design. The studies were conducted across a variety of settings, ranging from acute care to home. The international literature on the involvement of relatives of patients with acquired brain injuries comprises multiple published studies on different aspects of the topic and within various care contexts. The findings identified few studies describing wants and needs experienced by relatives in relation to involvement in the patient’s disease trajectory. Conclusions: The findings show that relatives’ wants and needs are primarily related to information and communication, but are also related to collaboration with health care professionals. The findings illustrate that the complexity of involvement is comprehensive, with multiple aspects to consider.