Many conservation interventions aim to influence people’s behaviour. Success depends upon a proper understanding of what motivates behaviour. I begin by reviewing social psychological models of behaviour, discussing how social psychological predictors of behaviour have been studied within conservation. Many studies focus on general attitudes towards conservation, rather than attitudes towards specific behaviours impacting on conservation success, assuming general attitudes are a useful indicator of behaviour, despite mixed evidence. Interventions depending upon rules require information about the quantity of people, and the types of people, breaking rules. However, when the subject of investigation is sensitive because it is illegal or socially taboo, it is naive to expect that people will respond honestly to questions about rule breaking when asked directly. Specialised methods exist for investigating sensitive topics yet are rarely used within conservation. I provide evidence that the randomised response technique (RRT) produces more accurate estimates of illicit behaviours compared to conventional surveys. Further, I show that RRT can be adapted to investigate how non-sensitive social psychological characteristics of respondents, such as their attitudes towards specific conservation-related behaviours, can be linked to their behaviour. This paves the way for using RRT to test the effectiveness of innocuous questions as proxy indicators for people’s involvement in illicit behaviours. There has been concern that sanctions for wildlife crimes do not reflect how serious crimes are in terms of illegal profits or the threat status of targeted species. Sanctions should reflect how serious a crime is, whilst being socially acceptable. I use conjoint analysis to understand public and professional opinions as to which aspects of wildlife crimes make them more or less serious, and so deserving of a greater or lesser sentence. Results highlight the gravity judiciaries place on illegal profits when setting sentences. Finally, to understand how sanctions relate to species threat status, I analyse 23 years of wildlife crime sanctioning from the United Kingdom providing evidence that sanction severity increases with threat status and corresponding legal protection. This thesis is an example of how expanding our knowledge beyond traditional academic boundaries can enhance the development of conservation science.