The party was formed on 14 October 1966 by a group of young academics led by Hans van Mierlo. The party had their most success in the 1994 election, where they won 24 out of 150 seats. In the 2010 elections, they received 654,167 votes and won 10 seats. In the 2012 elections they received 757,091 votes and won 12 seats. In the 2017 elections they won 19 seats (+7), and in the 2021 election 24 (+5).
D66 is very supportive of the European Union. They historically supported the legalization of gay marriage, prostitution, and euthanasia. The party supports environmentalism and wants a mixed economy. D66 wants tax-cuts for the lower and middle classes. They also want direct democracy.
- Hans van Mierlo - 1966-1973
- Jan Terlouw - 1973-1982
- Laurens Jan Brinkhorst - 1982
- Maarten Engwirda - 1982-1986
- Hans van Mierlo - 1986-1998
- Els Borst - 1998
- Thom de Graaf - 1998-2003
- Boris Dittrich - 2003-2006
- Alexander Pechtold - 2006-2018
- Rob Jetten - 2018-2020 (actually only parliamentary leader)
- Sigrid Kaag - 2020-