Additionality is a core aspect of quality assurance of greenhouse gas emissions reduction and sequestration activities, being used in a climate change context to mean net abatement over and above that which would have arisen anyway in the absence of a given activity or project. The underlying rationale of is to distinguish activities which further contribute to climate change mitigation from those which, although they may be associated with carbon savings, offer no benefits above those expected anyway. Different aspects of additionality are distinguished, and different approaches to testing for these and establishing associated baselines reviewed, in order to help inform development by the Forestry Commission of a Code of Conduct for forestry carbon projects in the UK.