This technical report aims to support the understanding and use of classical biological control for the management of invasive alien species that threaten biodiversity and ecosystem services, or already degrade or transform native ecosystems and natural environments. The report provides a detailed review of the history of the success, failure and cost effectiveness of classical biological control programs against the different taxonomic groups of invasive alien species across the agricultural and environmental sectors showing that the likelihood of success is quite target specific, but that the benefits are not always sector specific. There may be Joint benefits for both natural and agricultural ecosystems. The need to address ethical and societal acceptance of the introduction of another ‘beneficial” alien species to control an existing impactful invasive alien species is also explored to show how classical biological control has obtained public acceptance in some contexts and regions, but processes need to put in place to address such issues more broadly around the world. An ethical framework is proposed. Two sections cover existing national and international regulatory mechanisms and agreements supporting the application of biological control both at a national and regional level, while also identifying regulatory gaps. The report also provides a comprehensive review of direct and indirect non-target impacts from historical extant biological control programs and the risk factors (both perceived and real) that contribute to this. After a brief discussion of the future prospects of classical biological control for invasive alien species threatening or harmfully transforming environmental assets, the report concludes with an overview of what countries and jurisdictions, which do not currently or actively undertake classical biological control, need to consider in order to start to adopt such an approach and use classical biological control in the future, should they wish to consider it. This report also contains, in an unbiased manner, the information and inference based on the submissions from Parties and other Governments in response to the Convention on Biological Diversity notification 2015-0525. Click here for more info.