Background: Older adults are frequently hospitalized. Family involvement during these hospitalizations is incompletely characterized in the literature., Objective: This study aimed to better understand how families are involved in the care of hospitalized older adults and develop a conceptual model describing the phenomenon of family involvement in the care of hospitalized older adults., Methods: We describe the protocol of a qualitative evidence synthesis (QES), a systematic review of qualitative studies. We chose to focus on qualitative studies given the complexity and multifaceted nature of family involvement in care, a type of topic best understood through qualitative inquiry. The protocol describes our process of developing a research question and eligibility criteria for inclusion in our QES based on the SPIDER (Sample, Phenomenon of Interest, Design, Evaluation, and Research type) tool. It describes the development of our search strategy, which was used to search MEDLINE (via Ovid), Embase (via Elsevier), PsycINFO (via Ovid), and CINAHL Complete (via EBSCO). Title and abstract screening and full-text screening will occur sequentially. Purposive sampling may be used depending on the volume of studies identified as eligible for inclusion during our screening process. Descriptive data regarding included individual studies will be extracted and summarized in tables. The results from included studies will be synthesized using qualitative methods and used to develop a conceptual model. The conceptual model will be presented to community members via engagement panels for further refinement., Results: As of September 2023, we have assembled a multidisciplinary team including physicians, nurses, health services researchers, a librarian, a social worker, and a health economist. We have finalized our search strategy and executed the search, yielding 8862 total citations. We are currently screening titles and abstracts and anticipate that full-text screening, data extraction, quality appraisal, and synthesis will be completed by summer of 2024. Conceptual model development will then take place with community engagement panels. We anticipate submitting our manuscript for publication in the fall of 2024., Conclusions: This paper describes the protocol for a QES of family involvement in the care of hospitalized older adults. We will use identified themes to create a conceptual model to inform further intervention development and policy change., Trial Registration: PROSPERO 465617; https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023465617., International Registered Report Identifier (irrid): PRR1-10.2196/53255., (©Judith B Vick, Blair P Golden, Sarah Cantrell, Melissa Louise Harris-Gersten, Mollie R Selmanoff, Susan Nicole Hastings, Tolu O Oyesanya, Karen M Goldstein, Courtney Van Houtven. Originally published in JMIR Research Protocols (https://www.researchprotocols.org), 10.05.2024.)