<p>Early-stage venture funding has become a cornerstone of entrepreneurial ecosystems, with investors shaping venture outcomes and broader market dynamics. Yet, research on investor–investor dynamics remains fragmented across entrepreneurship, strategy, and finance. Existing studies typically examine collaboration and competition in isolation, limiting understanding of the conditions under which investors interact with one another through cooperation, competition, or hybrid strategies. This paper addresses the gap by conducting a PRISMA-based systematic literature review of 52 peer-reviewed studies, drawing on Scopus and Web of Science. We code the literature along structural, behavioural, and institutional antecedents to trace how investor relationships evolve across the funding lifecycle. Findings indicate that early rounds are dominated by collaboration through syndication, joint due diligence, and risk-sharing, whereas later rounds increasingly feature competition over valuation, governance, and exit strategies. We advance understanding of investor coopetition by explaining how syndication-based cooperation and governance-based rivalry systematically shift across funding stages. The review’s primary contribution is a new integrative framework that synthesizes the literature by linking the antecedents, dynamics, and outcomes of investor coopetition. Built on a transparent, replicable methodology, this framework illuminates critical research gaps, offers a detailed agenda for future inquiry, and provides practical insights for investors and policymakers.</p>