Forests are critical for the world's biodiversity, the regulation of the Earth's climate, and the provision of goods and services for humans. This review focuses on four broad topics: (1) key processes threatening forest biodiversity; (2) broad strategies for mitigating threatening processes; (3) climate change and forest biodiversity; and, (4) plantations and biodiversity. How key issues within these broad topics are addressed will have profound effects on forest biodiversity and the Earth's climate. A significant global problem for biodiversity conservation is the conversion of natural forests to other land uses, both in developing and developed nations; ways must be urgently identified to halt forest conversion. When forests are logged for timber or pulpwood and then regenerated, impacts on biodiversity are harder to quantify than when forests are converted to other land uses. Hence, the effectiveness of efforts to mitigate such impacts (where they occur) is frequently not well known. Climate change may result in substantial changes to forest ecosystems, and its effects may interact in additive or cumulative ways with other human disturbances in forests, although work on such combinations of impacts is in its infancy. The establishment of plantations of trees is frequently proposed to sequester large amounts of carbon and/or produce biofuels to mitigate the climate-change effects. However, there is potential for perverse outcomes, such as biodiversity loss where plantation establishment is narrowly focused and other environmental values are ignored.