Misinformation poses a significant threat to society, distorting public understanding of critical issues and undermining informed decision-making. From political falsehoods to health-related conspiracies, the pervasive spread of misleading information has far-reaching consequences. While much research on misinformation susceptibility has focused on cognitive factors - such as reasoning ability or analytical thinking - it often overlooks the social contexts in which judgements are made. This thesis addresses this gap by examining the role of social influence, specifically social proof, political identity and source effects, in misinformation susceptibility. Through a series of experiments and interventions, the thesis explores how the social context in which misinformation is consumed affects individual judgements of its veracity (Part I) and how this, in turn, influences the effectiveness of psychological interventions designed to reduce its impact (Part II). Chapter 1 introduces the problem of misinformation and offers a social-psychological perspective on how individuals process information. Building on this, the chapter presents inoculation theory as a potential solution to the misinformation problem while highlighting its limited testing in social environments. Chapter 2 presents two online experiments on source effects, demonstrating that news consumers are more susceptible to misinformation from (real) politically aligned media outlets, with this effect mediated via perceived source credibility. Chapter 3 presents a two-by-two experiment that demonstrates the causal impact of both source credibility and source similarity on misinformation susceptibility - even for fictitious news sources. Chapter 4 experimentally examines the effect of social cues, showing that individuals are more likely to believe misinformation when social proof - such as social media engagement - suggests that others find it reliable. Chapter 5 presents a gamified intervention study demonstrating that inoculation protects news consumers against misinformation from political ingroup news outlets. Chapter 6 presents an intervention study showing that a text-based inoculation intervention is effective in the presence of persuasive social cues, though even inoculated participants were influenced by these social cues. Chapter 7 discusses the broader implications of these findings and situates them within the existing literature, offering directions for future research. The research highlights how social context plays a powerful role in shaping people’s susceptibility to misinformation. This thesis further demonstrates that while inoculation theory is effective in reducing misinformation susceptibility, certain contextual cues continue to influence judgements, even in inoculated individuals. By providing a framework that integrates social identity theory, social influence research, and cognitive approaches, this thesis advances our understanding of how individuals process misinformation within social environments. These findings have significant implications for developing scalable interventions deployed across digital and social media environments, where much of today’s news consumption and interaction occur.