EU history timeline: the treaties and the dates to know

The treaties: signed, in force, and what each changed

The signing date is written into each treaty's final clause. The Coal and Steel Treaty, for example, closes like this:

Signed is not the same as in force

A treaty is signed by the member states' plenipotentiaries and then has to be ratified by every signatory. It enters into force only when the last instrument of ratification is deposited, or shortly after, as its final clauses specify.

The EEC Treaty chose a different rule: entry into force on the first day of the month after the last deposit, or of the second month if the deposit came less than fifteen days before the month's start (Article 247 EEC). The Single European Act used the first day of the month after the last deposit (Article 33). So almost every treaty has two years attached: Maastricht was signed in 1992 and entered into force in 1993; Nice was signed in 2001 and entered into force in 2003; the Single European Act was signed in 1986 and entered into force in 1987. One treaty, the Constitutional Treaty of 2004, was signed and never entered into force.

When a question asks for 'the year of' a treaty, read the stem for the verb. 'Signed', 'adopted' and 'entered into force' point to different rows of the table above.

Enlargements: from 6 to 28 members, and back to 27

Other dated milestones

The 2024 elections and the 720 seats

Members of the European Parliament are elected for five years by direct universal suffrage (Article 14(3) TEU). Article 14(2) TEU caps Parliament at 750 members plus the President, with at least six and at most 96 seats per member state. Within that cap, European Council Decision (EU) 2023/2061 of 22 September 2023 set the seats for the 2024-2029 parliamentary term. Its allocation adds up to 720: Germany 96, France 81, Italy 76, Spain 61, Poland 53, and 6 each for Cyprus, Luxembourg and Malta.

So the Parliament elected in 2024 has 720 seats, and the Treaty cap is a different number. The decision also asks Parliament to propose a new allocation for 2029-2034, if possible by the end of 2027. For every country's figure, see the numbers of the EU institutions.

The treaties' names in English, French and German

Candidates sit the internal test in their second language (English, French or German), so the German 'Vertrag von Nizza' and the French 'Acte unique européen' are worth knowing by sight. The glossary gives the three-language terms for the institutions and procedures.

How it is tested

Treaty history belongs to the EU's institutional set-up, one of the three content areas in the Commission's guidance to candidates. The dates themselves never change, so in our analysis the difficulty lies in the neighbours: a signing year offered next to the entry-into-force year, a treaty matched to a change made by the one before or after it, or an enlargement placed in the wrong decade. Learn each row of the first table as a pair of dates plus one change.

Worked example 1 (our own)

Which treaty created a single Council and a single Commission for the three European Communities? A. The Treaty of Rome establishing the EEC. B. The Merger Treaty. C. The Single European Act. D. The Treaty of Amsterdam.

Answer: B. Signed in Brussels on 8 April 1965, in force on 1 July 1967 (europa.eu, 'Founding agreements'). D is the treaty that later repealed it.

Worked example 2 (our own)

In which year did the Single European Act enter into force? A. 1985. B. 1986. C. 1987. D. 1992.

Answer: C. It entered into force on 1 July 1987 (europa.eu, 'Founding agreements'). B is the year it was signed, in Luxembourg and The Hague.

Test these dates under time pressure in the free 30-question test, with Commission or open-competition rules, AD or AST timing, in English, French or German, or try the daily quiz. For the institutions the treaties created, see the seven EU institutions compared; for the dates and numbers people most often get wrong, see the common traps. The competition page for COM/AD/111/2026 (AD6) shows how the test fits into the competition.