Appropriation of public lands associated with agricultural frontier expansion is a longstanding occurrence in the Amazon that has resulted in a highly skewed land-tenure structure in spite of recent state efforts to recognize tenure rights of indigenous people and smallholders living in or nearby forests. Growing concerns to reduce environmental impacts from agricultural development have motivated state governments to place greater attention on sustainable land management and forest conservation. This paper assesses the political and institutional conditions shaping tenure security and land appropriation in lowland Bolivia and the State of Pará in Brazil, and their links with environmental governance. The two cases show that clarifying and securing tenure rights is considered as the cornerstone for improving environmental governance. Thus, much attention has been given to the recognition of indigenous people and smallholder rights and to legalization of large-scale estates in agricultural frontiers, which have in turn influenced emerging conservation and environmental governance approaches. While policy frameworks share similar goals in the two cases, contrasting implementation approaches have been adopted: more agrarian in lowland Bolivia and more conservationist in the State of Pará.