Measuring Impact in Impact Investing: A Systematic Review of Approaches, Tensions, and Literature Gaps

Impact investing requires the assessment of social and environmental outcomes alongside financial returns, yet impact measurement remains methodologically fragmented and heterogeneous in purpose and use. This systematic review synthesizes the scholarly literature treating impact measurement as a central object of study within impact investing. Following PRISMA 2020 guidelines, records were identified through Scopus and Web of Science, screened at title/abstract and full-text stages, and appraised using design-specific quality criteria. The final corpus comprised 69 studies published between 2012 and 2026. Findings were synthesized narratively and complemented by descriptive bibliometric analysis. Four recurring themes emerged: persistent standardization efforts alongside methodological fragmentation; the growing role of ex-ante assessment; the organizational and relational functions of measurement; and contextual, institutional and organizational variation. The review further shows that impact measurement involves not only technical choices but also causal reasoning. Remaining evidence gaps concern the validation of ex-ante approaches, the use of impact information in actual investment decisions, external validation of measurement frameworks, and comparative evidence across institutional contexts.