Smoking remains the primary cause of preventable death and disease in the UK. Last year alone, 96,000 people in the UK died prematurely as a direct result of smoking and more than double this number of children took up smoking to take their place. As the 'average' smoker, smoking 12 cigarettes per day, will view their cigarette pack at least 4,300 times a year, the cigarette pack offers governments a unique tool to communicate the health impacts of smoking. The introduction of standardised (i.e., plain) packaging of cigarettes in the UK will mean that health warnings on packs are more noticeable. However, in order for this landmark legislation to be effective, these health warnings need to be sending out the right messages. Although health warnings with strong, threatening images and messages are used on cigarette packs in over 100 countries, there is evidence that smokers may avoid them or react negatively towards them. Theory suggests that warnings are most likely to result in positive behaviour change if they combine threatening messages with those which increase a smoker's perceived ability to stop smoking and knowledge of the benefits of stopping (known as 'efficacy' messages). Despite this, there has been very little research on the impact of efficacy messages on tobacco warnings, no research on how adolescents respond to efficacy messages and almost no adoption of efficacy messages on tobacco warnings globally. This project will address these key issues by examining responses to warnings with 'efficacy' and 'threatening' content and developing research on what constitutes effective warnings. This research is critically important given the potential for health warnings to educate individuals about the risks of smoking and encourage them to stop. It will apply a strong theoretical framework to examine the roles of efficacy and threatening content on warnings among both adults and adolescents. Given that two-thirds of smokers start before the age of 18, there is surprisingly little research on the impact of warnings among adolescents. My research will address this critical gap in the literature. This project is timely and important, not only because of the recent introduction of standardised packaging of cigarettes. Britain's exit from the EU will provide the UK government with a unique opportunity to implement new warnings and strengthen tobacco control policies, as these will no longer be enforced by the EU-wide Tobacco Products Directive. I will conduct online surveys among adults and adolescents smokers. These surveys will examine, for the first time, responses to threatening and efficacy warnings and their impact on attitudes towards smoking. I will then use the findings of these studies to conduct two 'mixed methods studies' among adults and adolescents to measure self-reported reactions, brain activation and smoking behaviour in response to health warnings. My research uses a unique combination of innovative approaches combining subjective and objective techniques. This research is novel in a number of ways. First, it will provide objective and previously unexplored insights into differences in response to warnings among adults and adolescents. Second, it will develop our understanding of the mechanisms underlying responses to efficacy and threatening warnings. Finally, it will produce the first evidence demonstrating how neural and subjective responses to warnings are related and how these predict longer-term smoking behaviours and attitudes. This research will support the development of better, more effective warnings for tobacco products and provide a toolkit for the development of effective warnings for a range of unhealthy products, such as alcohol and unhealthy food, which can be used by academics and policymakers internationally. This project ultimately aims to reduce the rates of premature death and disease caused by smoking by providing evidence to support tobacco packaging policy change.