This Practice Note looks at biodiversity net gain (BNG) from an environmental consultant’s perspective. It covers: how BNG works in practice; how biodiversity units are calculated; good practice principles for BNG, such as following the mitigation hierarchy, avoiding the loss of biodiversity that cannot be offset elsewhere, engaging stakehoders, addressing risk, achieving the best outcomes for biodiversity, creating a net gain legacy, and optimising sustainability; the stages of the BNG process; and common challenges of delivering BNG in practice.