The concept of additionality, when public interventions are considered, can be synthesised as the net effects that would not have occurred in the absence of the intervention of the public actor. The present paper reviews the body of literature dealing with the concept of additionality, devoting particular attention to its behavioural dimension (i.e. changes in beneficiaries' behaviours resulting from the policy intervention). In the first sections it is stressed that the behavioural additionality, though not yet clearly defined and still characterised by some drawbacks, complement the input and output dimensions of the concept of additionality and can be used to evaluate innovation policies according to the evolutionary and system perspectives. In the subsequent sections we present a review of the recent econometric and quantitative studies focused on the behavioural additionality in order to present a state of the art of the methods, with their limits and thei strengthens, that can be used in this kind of evaluation.