“Voluntary party quotas have been increasingly popular among left and centre-left parties such as Green, Socialist and Social Democratic parties […] in many countries in Europe. In Sweden, many political parties introduced voluntary party quotas in the form of a ‘neither sex should be represented by less than 40 per cent’ rule in 1970s and 1980s, as a result of which the number of women MPs reached 39 per cent in the 1988 elections. It was only after the 1991 elections (when women’s numbers in parliament dropped to 34 per cent) that women in various parties demanded stricter measures, such as alternating between male and female candidates across candidate lists, in order to secure true parity among elected representatives. Voluntary party quotas contributed to significant advances in the representation of women in national parliaments in countries as diverse as Australia, Germany, Mozambique, Namibia, Nicaragua, South Africa and the United Kingdom. […] In about 37 countries and territories one or more parties use voluntary party quotas.[1] 

Any political party can introduce gender quotas for their own lists for public elections. One or two parties can be forerunners for other parties in a country. In many countries, gender quotas were first introduced by individual political parties, and were later adopted by parliaments with binding quota regulations for all political parties.[2] 

Voluntary party quotas applied to candidate lists should be complemented by ranking- order provisions in order to ensure that women are included in leading positions of the candidate lists and evenly distributed across the entire list of candidates.[3] 

Voluntary quotas are likely to be respected and properly implemented in parties with clear rules, a bureaucratic culture and standardized practices […]. Hence, highly institutionalized parties may provide a more conducive environment for adopting and implementing voluntary party quotas.”[4]