Private nature reserves created by non-governmental organizations (NGOs) are increasing, and their growing number and extent means that they can potentially contribute to biodiversity goals at a global scale. However, the success of these reserves depends on the legal, economic and institutional conditions framing their creation and management. We explored these conditions, and the opportunities and challenges facing conservation organizations in managing private nature reserves, across several countries, with an emphasis on Australia. Results from 17 semi-structured interviews with representatives of private conservation organizations indicated that while private reserves may enhance the conservation estate, challenges remain. Legal frameworks, especially tenure and economic laws, vary across and within countries, presenting conservation organizations with significant opportunities or constraints to owning and/or managing private nature reserves. Many acquired land without strategic acquisition procedures and secured funding for property acquisition but not management, affecting the long-term maintenance of properties. Other typical problems were tied to the institutional capacity of the organizations. Greater planning within organizations, especially financial planning, is required and NGOs must understand opportunities and constraints present in legislative frameworks at the outset. Organizations must establish their expertise gaps and address them. To this end, partnerships between organizations and/or with government can prove critical.