Despite efforts to reverse the current global environmental crisis that threatens biodiversity and human well-being, many indicators suggest we are still far from changing the main trajectory towards sustainability. With privately owned land covering large areas of the world, private land conservation (PLC) has been recognized as a promising strategy to complement protected area networks in meeting biodiversity conservation objectives. However, the overall success of PLC depends on designing and implementing a suite of policies according to geographical contexts and to the needs, values, and capabilities of different stakeholders. In my doctoral thesis, I aim to identify challenges and opportunities to foster PLC at different geographical scales by understanding the main trends and gaps in a global PLC literature review and by assessing landowners’ preferences and needs at national and local levels. In order to do so I followed transdisciplinary approaches, combining theories and methods from the natural and social sciences in collaboration with stakeholders outside academia. In the first chapter, I carried out an in-depth global literature review of PLC scientific articles. My results revealed that most studies have focused on limited geographical contexts and policies. This highlighted the need for i) assessing a more diverse set of policy instruments to increase participation; ii) increasing stakeholders’ engagement in research to better inform PLC policymaking; iii) better understanding barriers and opportunities to foster PLC in underrepresented regions, such as South America. Based on findings from my first chapter, I conducted two empirical studies at local and national levels in Uruguay, a country where most of the land is privately owned (~96%). While the importance of voluntary PLC has been recognized by law in 2017, in Uruguay PLC policy has not been developed or implemented yet. Hence, there is a need to understand context-specific landowners’ preferences for voluntary PLC to inform policy-making at early stages. In the second chapter, I applied qualitative methods to explore landowners´ perceptions, motivations and needs for voluntary conservation in a cultural landscape in north-eastern Uruguay. I found that landowners considered themselves and their neighbours as local environmental stewards and their main needs to support biodiversity conservation were mostly related to enhance land management and social cohesion. My results revealed that strengthening existing links between people and nature and addressing local rural development needs could confer both social and conservation benefits in a just and sustainable way. In the third chapter, I used stated preference methods to assess landowners’ preferences for hypothetical voluntary PLC policies at the national level in Uruguay. My results revealed that landowners had high willingness to engage in voluntary conservation initiatives if future policies would meet their heterogeneous preferences. Offering a diverse set of policy instruments, mainly non-monetary incentives, while fostering networks and collaboration with different stakeholders could help increase participation and long-term engagement in voluntary PLC. To conclude, by following a transdisciplinary approach my thesis contributes to identifying and addressing research gaps in PLC at different scales with practical implications for biodiversity conservation, sustainability, and policymaking in Uruguay and elsewhere in the world in similar contexts. In addition, my thesis highlights the need for future research to disentangle the main contextdependent dimensions driving PLC effectiveness but also to identify general principles that could inform the design, governance and implementation of legitimate and equitable policies across contexts.