Project 5.1 Biodiversity offsetting is increasingly used as a mechanism to compensate unavoidable development impacts on biodiversity. Yet, major knowledge gaps exist in how best to calculate both development impacts and offset benefits for biodiversity, particularly for poorly known species and communities. This large project will develop and test new guidance and protocols for the most challenging aspects of offsetting impacts on threatened species. In particular, we focus on: 1) robust estimation of the benefit of habitat protection; 2) identifying novel and cost-effective offset approaches for species and communities that commonly trigger offset requirements, but for which offsets are particularly challenging; and 3) exploring approaches that can deliver improved benefits through more strategically targeted and coordinated actions. In combination, this will improve offset benefits to nationally threatened species and ecological communities.