Since the constitutional referendum of the Batavian Republic in 1805, only three referendums have been held. The first was the consultative, "ad hoc" referendum on the European Constitution in 2005. The second was the referendum on the ratification of the Ukraine–EU Association Agreement on 6 April 2016, which was the first referendum under the Advisory Referendum Act. On 21 March 2018, the 2018 Dutch Intelligence and Security Services Act referendum was held.