Governments, companies, banks and civil society are placing more emphasis on the rigorous application of the mitigation hierarchy to avoid, minimize and compensate for projects' impacts on biodiversity. The final step in the mitigation hierarchy sequence are biodiversity offsets to achieve No Net Loss (NNL) or Net Gain (NG). Thirty-nine countries have existing laws or policies on NNL/NG, biodiversity offsets or compensation, and twenty-two countries are developing them. The purpose of this paper is to contribute to the consideration of policy options by the IUCN Technical Study Group on biodiveristy offsets and the subsequent Working Group and to provide information more broadly to governments and their advisors. It is intended as a basic introduction to policy on NNL or NG of biodiversity and biodiversity offsets.