The current program of research contributes to the World Health Organisation's (WHO, 2004) recent call to pool global resources in the attempt to uncover the most effective countermeasures and polices for the prevention of road trauma. Specifically, this program of research investigates the persuasive outcomes of different emotional health messages in an important applied context, road safety. In this context the use of negative, fear-based approaches has predominated with limited use of more positive-based approaches such as humorous- or pride-based emotional appeals. The overarching aim of the current research program was to examine the effectiveness (i.e., persuasiveness) of positive and negative emotional appeals and, specifically, the issue- or message-relevant affect that such appeals evoke. An additional aim was to ascertain the relative influence and effectiveness of positive and negative emotional appeals for specific target audiences. Particular attention was given to the effectiveness of such messages for males, a high risk road user group of particular concern. The research program also aimed to examine the relative roles and interplay of emotion and cognition in determining message effectiveness. The research focused upon the cognitive constructs of response efficacy (i.e., the extent to which a message incorporates coping strategies and information as well as the extent that individuals' perceive a message as incorporating such coping strategies and information) and involvement (i.e., the extent to which individuals perceive an issue or message as personally relevant and/or as being at risk of experiencing).----- The research program may be conceptualised as three stages, with each stage comprised of an empirical study and one or more manuscripts. The first stage of the research explored the roles and effectiveness of negative and positive emotional appeals. With a substantial body of literature available on the use of fear as a persuasive strategy, Paper One reviewed the theoretical and empirical evidence relating to the function and effectiveness of such appeals. This paper highlighted the mixed findings that have been reported and the controversy surrounding the nature of the fear-persuasion relationship. This paper also highlighted the importance of cognitive components of a message and, in particular, the need to incorporate high levels of response efficacy and to be cognisant of the issue of threat and message relevance.----- Paper Two was based on qualitative research derived from focus groups of licensed drivers (N = 16). The study investigated the roles and effectiveness of positive and negative emotional appeals in road safety advertisements addressing speeding and drink driving. The results suggested that positive and negative emotional appeals may serve different functions. Positive emotional appeals were regarded as a potentially efficacious means of promoting the message of prevention and to model safe behaviour and the rewards received whereas negative emotional appeals were regarded an important way to remind drivers of the dangers of driving.----- The second stage of the research program endeavoured to extend upon the findings reported in the first stage by providing an empirical comparison of positive, humorous appeals and negative, fear-based appeals on a range of outcome measures and over time. In Paper Three, the type of emotional appeal (positive/humorous, negative/fear), level of response efficacy (low, high), level of involvement (low, high), and gender were manipulated in a 2 x 2 x 2 x 2 mixed group design. Licensed drivers (N = 201) completed either a paper-and-pencil or internet-based version of a questionnaire. Prior to the anti-drink driving television advertisements being shown, pre-exposure were assessed. Attitudes and intentions were then assessed immediately after exposure and attitudes, intentions, and behaviour, 2 to 4 weeks later. The results provided evidence of the greater persuasiveness of negative appeals immediately after exposure and greater improvement of positive appeals over time. Also, the results highlighted the importance of high levels of response efficacy, irrespective of emotional appeal type. Paper Three also supported and extended upon earlier findings by examining third-person perceptions in relation to positive, humorous emotional appeals. The results revealed that males reported significantly greater overall influence both to themselves personally, as well as other drivers in general, than females for the humorous appeals. Further, consistent with the multiple roles of affect posited by Elaboration Likelihood Model, explanations were provided for the differential effectiveness of positive and negative affect.----- An additional aim of the second stage of the research program was to clarify an important methodological issue; the sampling adequacy of traditional university student samples versus internet-based samples for health message persuasion research. Fear appeal empirical literature has been criticised for its over-reliance upon student samples. Paper Four examined the extent that the internet may function as an efficacious means of accessing drivers for road safety advertising research. The sample characteristics and results obtained from student and internet samples of drivers were compared empirically. The results provided support for the greater diversity and representativeness of the internet sample and suggested that the two sampling approaches produce equivalent results. This paper served to inform the validity of prior research and informed the choice of sampling methodologies for the subsequent research stage reported in Paper Five.----- The third stage of the research built upon the preceding stages and, most notably, broadened the scope of emotional appeals examined by comparing a range of negative and positive emotional appeals addressing the issue of speeding. Drawing upon the Rossiter-Percy (1987, 1997) motivational model, Paper Five examined two different negative and two positive emotional appeals designed as audio messages. Specifically, the type of emotional appeal (Problem Avoidance/Fear based; Problem Removal/ Agitation or annoyance-based; Social Approval/ Pride-based; and Intellectual Mastery/ Humour-based), level of response efficacy (low, high), level of involvement (low, high), and gender were manipulated in a 2 x 2 x 2 x 2 fully between groups design. A range of persuasion outcome measures, including attitudes and intentions, were assessed immediately after exposure and 1 month later. Further, the study assessed adaptive (message acceptance) as well as maladaptive (message rejection) intentions. The results provided evidence of the effectiveness of humorous-based appeals for males and highlighted that appeals of the same valence (positive or negative) need not have the same persuasive effects. The results also supported the importance of response efficacy for all appeal types and highlighted that a message's overall effectiveness requires consideration of both message acceptance and rejection rates.----- Overall, the current research program, based upon a sound, multi-disciplinary theoretical framework, provided evidence for the need to broaden the scope of emotional appeals in the road safety advertising context and which may also be relevant within a wider health persuasion context. The results of the three studies have important theoretical and practical implications for future campaign development which are discussed.