Objective:The research investigated whether a stronger predictive model of volunteering behaviour prevails when the functions of the volunteer functions inventory are combined with the constructs of the theory of planned behaviour. The study advances on prior research which either examined the predictive capacity of each model or compared their explanatory values. Method: The survey was completed by 186 individuals (Male = 56.10%; Mean Age = 63.7 years) who were retired or approaching retirement and within the context of episodic, skilled volunteering. Results: Multiple regression analyses found that the functions of the volunteer functions inventory explained a further 7% of variability in individuals' willingness to volunteer, over and above that accounted for by the theory of planned behaviour. Within the final model, which explained 62% of variability in willingness to volunteer, significant predictors included attitudes, subjective norms and perceived behavioural control (from the theory of planned behaviour) and the understanding function from the volunteer functions inventory. Items representing the understanding function are proposed to represent a deeper psychological construct (e.g., self-actualisation) not accounted for by the theory of planned behaviour. Conclusions: The findings highlight the potential benefit to be gained from the amalgamation of these two prominent models in terms of improving understanding of volunteerism and providing a single parsimonious model for use in research and practice. Extending the research to include a broader range of volunteering contexts and populations will validate the benefit of combining the models.Key words: episodic volunteering, older people, self-actualisation, theory of planned behaviour, volunteer functions inventoryThe study of volunteerism has taken a variety of paths in an attempt to strengthen the understanding of the behaviour and to establish the most effective means of influencing its occurrence across diverse populations and settings. Indeed, the understanding of volunteering has been enhanced in recent times by examining the behaviour from a broader range of theoretical perspectives (see Wilson, 2012). The volunteer functions inventory (VFI; Clary et al., 1998), a prominently applied theory within volunteering research (Hustinx, Cnaan, & Handy, 2010), has played an instrumental role in advancing knowledge of intrinsic motivation to volunteer across many contexts. Acknowledging that volunteering is an act influenced by factors both intrinsic and external to the individual, the theory of planned behaviour (TPB; Ajzen, 1991) also provides researchers with a framework for assessing individual and contextual determinants of the behaviour. In addition to examining the respective explanatory value of these two models in isolation, previous volunteering studies have also compared the predictive capacity of the two frameworks (e.g., Greenslade & White, 2005), at times positioning the theories in opposition to one another. To date, however, the explanatory...