Livelihood interventions are often implemented in villages adjacent to protected areas with the aim of reducing the biodiversity impacts of local livelihood practices by promoting substitute activities. Despite uncertainty regarding the effectiveness of these so-called ‘alternative livelihood projects’, they still remain a go-to strategy in both the terrestrial and marine conservation realms. In this thesis, I critically reflect on the role of livelihood interventions in conservation by examining key assumptions made during their design and implementation, their mechanisms of impact, and the social-ecological systems in which they are embedded. Drawing insights from livelihoods research and behavioural science, I specifically investigate how livelihood projects aimed at reducing bushmeat hunting in Cameroon function in practice and consider how a broad range of factors influence livelihood decision making. Using qualitative research methods, I compare the perceptions and experiences of participants and implementers in relation to twenty alternative livelihood projects implemented around two protected areas. I scrutinise the theories of change underlying these projects and explore where breakages in the chain of logic occur. Using a comprehensive behavioural science theory – the COM-B model – as a diagnostic framework, I identify barriers to behaviour change as well as potential enablers. I then present an illustrative case study focused on urban-based out-migrants to demonstrate the importance of intervention targeting by highlighting how natural resource use and reliance can differ between community sub-groups, and the ways in which this can evolve under different economic scenarios. My research shows that key assumptions, such as those based on the notions of substitution, the homogenous community and impact scalability, are flawed. The development of more nuanced and realistic theories of change that clearly articulate how interventions are expected to have an impact is critical to enable greater scrutiny and further develop an evidence base for what works. Project implementers typically underestimate the time and resources required, as well as the complexity, of intervening to alter people’s livelihood strategies. Motivation is key to determining whether promoted livelihood practices are adopted, yet what motivates people to do what they do is often overlooked. Moderating expectations and integrally involving the resource users to be targeted from the outset is essential. Livelihood interventions require deep thought, collaboration, a thorough analysis of the situation, more precise targeting and a greater understanding of livelihoods and behaviour change processes to be effective. Factors that can enhance or limit a project’s impact are outlined in a set of guiding principles to inform the design and implementation of livelihood interventions moving forward.