There is growing evidence of the inter-relationships between ecosystems and public health. This creates opportunities for the development of cross-sectoral policies and interventions that provide dual benefits to public health and to the natural environment. These benefits are increasingly articulated in strategy documents at national and regional level, yet implementation of integrative policies on the ground remains limited and fragmented. Here, we use a workshop approach to identify some features of this evidence-implementation gap based on policy and practice within a number of western European countries. The driving forces behind some recent moves towards more integrative policy development and implementation show important differences between countries, reflecting the non-linear and complex nature of the policy-making process. We use these case studies to illustrate some of the key barriers to greater integrative policy development identified in the policy analysis literature. Specific barriers we identify include: institutional barriers; differing time perspectives in public health and ecosystem management; contrasting historical development of public health and natural environment disciplinary policy agendas; an incomplete evidence base relating investment in the natural environment to benefits for public health; a lack of appropriate outcome measures including benefit-cost trade-offs; and finally a lack of integrative policy frameworks across the health and natural environment sectors. We also identify opportunities for greater policy integration and examples of good practice from different countries. However, we note there is no single mechanism that will deliver integrative policy for healthier people and ecosystems in all countries and situations. National governments, national public agencies, local governments, research institutions, and professional bodies all share a responsibility to identify and seize opportunities for influencing policy change, whether incremental or abrupt, to ensure that ecosystems and the health of society are managed so that the interests of future generations, as well as present generations, can be protected.