Scaling of effective innovations in health and social care is essential to increase their impact. We aimed to synthesize the evidence base on scaling and identify current knowledge gaps. We conducted an umbrella review according to the Joanna Briggs Institute Reviewers' Manual. We included any type of review that 1) focused on scaling, 2) covered health or social care, and 3) presented a methods section. We searched MEDLINE (Ovid), Embase, PsycINFO (Ovid), CINAHL (EBSCO), Web of Science, The Cochrane Library, Sociological Abstracts (ProQuest), Academic Search Premier (EBSCO), and ProQuest Dissertations & Theses Global from their inception to August 6, 2020. We searched the gray literature using, e.g., Google and WHO-ExpandNet. We assessed methodological quality with AMSTAR2. Paired reviewers independently selected and extracted eligible reviews and assessed study quality. A narrative synthesis was performed. Of 24,269 records, 137 unique reviews were included. The quality of the 58 systematic reviews was critically low (n = 42). The most frequent review type was systematic review (n = 58). Most reported on scaling in low- and middle-income countries (n = 59), whereas most first authors were from high-income countries (n = 114). Most reviews concerned infectious diseases (n = 36) or maternal-child health (n = 28). They mainly focused on interventions (n = 37), barriers and facilitators (n = 29), frameworks (n = 24), scalability (n = 24), and costs (n = 14). The WHO/ExpandNet scaling definition was the definition most frequently used (n = 26). Domains most reported as influencing scaling success were building scaling infrastructure (e.g., creating new service sites) and human resources (e.g., training community health care providers). The evidence base on scaling is evolving rapidly as reflected by publication trends, the range of focus areas, and diversity of scaling definitions. Our study highlights knowledge gaps around methodology and research infrastructures to facilitate equitable North-South research relationships. Common efforts are needed to ensure scaling expands the impacts of health and social innovations to broader populations.