Initially, its main objective had been to democratise the Dutch political system, but it developed a broader social liberal ideology over time.

D66 is especially popular among people who hold a university degree, and its voters are mostly concentrated in larger cities and in municipalities with an above-average number of wealthy residents.

[9] Paul van Meenen, Rob Jetten and Gerben-Jan Gerbrandy are serving as the party's parliamentary leaders in the Senate, the House of Representatives and the European Parliament respectively.

It called for radical democratisation of the Dutch political system, and for pragmatic and scientific policy-making.

In the 1972 general election, the three parties formed a political alliance called the "Progressive Agreement" (Dutch: Progressief Akkoord; PAK) and presented the common electoral program "Turning Point '72" (Keerpunt '72).

In the period 1972–1974, the party lost a dramatic number of members (from 6,000 to 300) and polled very poorly in the 1974 provincial elections.

In reaction, Terlouw started a campaign to revitalise the party, involving a membership drive and a petition to the electorate.

D66 was able to form its preferred coalition: the "purple government", which included both the social democratic PvdA and the conservative liberal VVD.

As advocated by D66, the first Kok cabinet initiated progressive legislation, such as the introduction of same-sex marriage and the legalisation of euthanasia.

Shortly before the 1998 general election, Van Mierlo stepped back and Minister of Health Els Borst became the new top candidate.

In 1999, a constitutional reform that would allow for referendums to be held was rejected by the Senate, because a group of VVD dissidents had voted against it.

In the 2002 general election, the tide had turned against the purple government, and the right-wing populist Pim Fortuyn List (LPF) gained considerable ground.

The legislation had been introduced by the second Kok cabinet, but it was unable to get a two-thirds majority because the Labour Party was opposed the electoral system proposed by Minister for Governmental Reform Thom de Graaf.

De Graaf resigned, but the rest of the ministers retained their positions as D66 was promised more investment in public education and the environment.

In February 2006, Dittrich stepped down as parliamentary leader, because he did not agree with the government's decision to send the Dutch armed forces to the southern province of Uruzgan in Afghanistan.

D66 began to lose a considerable number of members, some of whom founded deZES, another radical democratic, progressive liberal party.

During the special parliamentary debate on the naturalisation process of Ayaan Hirsi Ali, D66 supported a motion of no confidence against Minister for Integration Rita Verdonk.

On 3 July 2006, the two D66 ministers Alexander Pechtold and Laurens Jan Brinkhorst resigned, causing the second Balkenende cabinet to fall.

Van Mierlo declared his support for party leader Pechtold, who in his view could provide for such credibility.

The news programme Nova attributed this increase to the leadership of Alexander Pechtold, who was considered "the leader of the opposition" at the time.

In the 2017 general election, D66 won 19 seats in the House of Representatives and formed a centre-right coalition government with the VVD, CDA and Christian Union (CU).

[19] Following the 2023 Dutch general election D66 lost more seats than any party, being reduced from 24 to 9, their worst result in 17 years.

The first party congress emphasised radical democratisation of Dutch society and the political system.

The electoral reform was gradually moderated as the party now favours German-style mixed member proportional representation.

[citation needed] D66's progressive liberal section has historically been much weaker than its radical democratic wing.

National political reasons explain the usage of the label "social-liberal" since the more right-leaning VVD describes itself as the liberal party.

In the 2014 municipal elections, D66 became the largest party in many major cities including Amsterdam, The Hague, Utrecht, Tilburg, Groningen, Enschede, Apeldoorn, Haarlem, Amersfoort and Arnhem.

The name referred to the party's goal of radical democratisation and to the year of foundation, which was supposed to convey a modern image.

In 1981, the apostrophe was dropped: the name had become a successful political brand, but the year no longer conveyed a modern image.

The youth wing of D66 is called the Young Democrats (Dutch: Jonge Democraten, abbreviated JD).