Additionality is one of the principles driving the workings of the European Structural and Investment Funds. This principle stipulates that contributions from the Funds must not replace public or equivalent structural expenditure by a Member State in the regions concerned by this principle. In other words, the financial allocations from the Structural and Investment Funds may not result in a reduction of national structural expenditure in those regions, but should be in addition to national public spending. The principle of additionality is verified in Member States where less developed regions cover at least 15 % of the population because of the scale of the financial resources allocated to them.
At the beginning of the programming period, the level of expenditure that the Member State will maintain throughout the programming period is set out in the Partnership Agreement ('ex ante' verification). The Commission will verify each Member State's compliance with the principle of additionality at the mid-term of the programming period, in 2018, and after the end of this period, in 2022.