OBJECTIVE: The ISPOR Patient Centered Special Interest Group established a Patient Engagement in Research Working Group to determine best practices for patient engagement in research. The group determined it was important to begin by standardizing terms and definitions for use in ISPOR work and communications. As a foundation, the objective of this study was to identify existing definitions for “patient engagement,” “centeredness,” and related terms in the context of research and health care decision-making. METHODS: A search of the grey and peer-reviewed literature, and internet was conducted. Search terms, English only, included: patient engagement, consumer engagement, patient involvement, patient cent*, consumer cent*, person cent*. Literature was searched for all years using PubMed and EMBASE. Google site:search was employed to search the internet; to target that search, experts identified domains for umbrella patient-advocacy, government, and other organizations prominent in patient engagement. Results were assessed for relevance by three research assistants with duplication for reliability. Inclusion criteria required: a definition for patient centeredness, patient engagement, or a related pre-specified term, and association with health care research or provision. Data were abstracted and analyzed using grounded theory methods. RESULTS: CONCLUSIONS: Numerous definitions of patient engagement and patient centeredness from multiple stakeholders are aimed at involving the patient in research and health care decision-making. As the ISPOR Patient Centered Special Interest Group examines these themes, they will guide consensus on developing an ISPOR definition for patient engagement and patient centeredness.