There has been substantial interest in examining socio-psychological determinants of veganism. However, there remains inconsistency within the literature and public discourse on the definition of veganism. This can be an issue for measurement, and comparison across studies. A mixed methods approach aimed to evaluate both existing definitions of veganism and respondent provided definitions to provide a groundwork for future studies in attitudes towards vegans and veganism. Study one (N = 620) was a quantitative study that investigated vegan, vegetarian, and omnivore opinions on existing definitions from vegan societies. Study two (N = 520) was a qualitative study that examined respondent provided definitions. These two studies also aimed to compare similarities and differences across the three dietary groups. The relevance of this work to promoting the reduction in meat and other animal product consumption, and implications for measurement, will be discussed.