Intense exploitation of our oceans and seas is degrading marine biodiversity and ecosystems at an alarming rate. This report presents good practice insights for effectively managing marine protected areas (Mpas), one of the policy instruments available for the conservation and sustainable use of marine biodiversity and ecosystems. While global coverage of Mpas has been increasing over the past two decades, further efforts are required to meet the target under the Sustainable Development Goals and to ensure they are effective. Drawing on the literature and numerous examples from developed and developing countries, this book highlights how the environmental and cost effectiveness of Mpas can be enhanced. It covers issues including the benefits and costs of Mpas, the need for more strategic siting of Mpas, monitoring and compliance, sustainable finance for Mpas, and the need to embed these in a wider policy mix so as to address the multiple pressures on marine ecosystems.