The goal of biodiversity offsets -- measurable conservation outcomes resulting from actions designed to compensate for significant residual adverse biodiversity impacts arising from project development after other appropriate prevention and mitigation measures have been taken -- is to achieve no net loss (or net gain) in biodiversity. This report assesses the conditions under which biodiversity offsets may provide the best outcomes for biodiversity and achieve no net loss. It was developed as an input paper to inform the IUCN Technical Study Group on Biodiversity Offsets and is intended as a basic introduction to technical issues related to offsets.