Marine spatial misinformation is a new type of digital misinformation that is created through manipulation or misinterpretation of marine geospatial information or its strategic messaging with reference to maritime boundaries, resource claims and ocean governance. The United Nations Convention on the Law of the Sea has given rise to the territorialization of maritime space that has implications for the location and representation of boundaries, both in terms of sovereignty and economic access and diplomacy (Balsano, 2025; Østhagen, 2020). In parallel, the utility of marine spatial knowledge (MSK) has increased, and ocean geospatial knowledge has become more sensitive thanks to Geographic Information Systems, satellite data, ocean geoportals and social media (Swilling et al., 2022; Davret & Trouillet, 2025). This chapter proposes a cross-disciplinary conceptual framework and summarises 45 key texts in political geography, international law, marine policy, media studies and information science. It then takes a literature synthesis method suitable to an emerging discipline that has a variety of terms, and recognises four intermingled mechanisms: cartographic manipulation, digital amplification, strategic ambiguity, and institutional failure. Comparative cases from the South China Sea, Eastern Mediterranean, Arctic and Chagos Archipelago illustrate the impact of these mechanisms on trust, sovereignty, maritime diplomacy, ecological management, and decolonisation. The chapter proposes, as a starting point for more resilient ocean governance, approaches that are critical for geospatial and ocean literacy, clear and open cartographic processes, ethical approaches to data control, approaches to responsible publishing norms, and approaches to collaborative digital platforms.