The federal popular initiative (German: Eidgenössische Volksinitiative, French: Initiative populaire fédérale, Italian: Iniziativa popolare federale, Romansh: Iniziativa federala dal pievel), is a Swiss civic right enabling 100,000 citizens with voting rights to propose a total or partial amendment to the Federal Constitution and submit it to a popular vote. The citizens behind the initiative, grouped together in an initiative committee, have 18 months in which to gather the approval of 100,000 citizens. To do this, the 100,000 citizens must affix their handwritten signatures to a signature list, including the text and title of the popular initiative. If 100,000 signatures are collected within 18 months, the initiative is put to the vote. If this is not the case, the initiative is declared "unsuccessful" and the procedure is terminated. The right of initiative also has its counterpart at cantonal and communal level; the procedure, including the number of signatures required and the deadline for collecting them, varies from one sovereign Swiss canton to another.

First used in 1893, the federal popular initiative has gradually developed over time to become one of the main means of expression for political parties or groups, used to bring about constitutional change without having to consult or obtain the approval of the federal authorities. From its inception to 2018, 215 such votes were held, an average of 1.69 per year. Although unlikely to be successful (around 10% of popular initiatives put to the vote are accepted), the federal popular initiative makes it possible to provoke public debate on issues that are not always addressed in traditional parliamentary debates. In addition, the federal parliament may oppose the initiative with a direct or indirect counter-proposal, which may or may not take up part of the initiative's demands.

From time to time, the advantages and disadvantages of the federal popular initiative are debated: public awareness of certain issues and the possibility of making demands that go beyond the priorities set by the authorities are set against the risk of this tool being used by demagogic and well-organized groups, and the considerable financial resources required for the popular vote campaign.

The most widely used form of federal popular initiative is a procedure whereby 100,000 Swiss citizens can draft a new constitutional article, or amend an existing one, and submit this constitutional amendment to a vote of the people and the cantons. The initiative is presented in the form of a draft bill. The popular initiative also exists in other forms, but these are rarely used in practice (initiative requesting a total revision of the Constitution, and initiative presented in the form of a general draft). It is formally defined in Articles 138 and 139 of the Federal Constitution. In practical terms, a federal popular initiative can therefore take three different forms:

The federal popular initiative is a tool specifically designed to propose amendments to the Federal Constitution. It does not have the power to directly modify federal laws or lower-level regulations. However, a successful popular initiative that alters or introduces a constitutional article may necessitate subsequent legal changes. This is true if the newly approved article includes provisions that are not self-executing (i.e., do not directly take effect without further legislation). In such cases, the popular initiative indirectly prompts amendments to federal laws, as these amendments would be required to implement the new constitutional article.

In the vast majority of cases, federal popular initiatives are presented in the form of a draft proposal. Of the 150 or so federal popular initiatives put to the vote before the end of the 20th century, only two were accepted by Parliament in the form of a general draft, and four (out of a total of 11 proposals) were put to the vote (for the revision of the alcohol regime in 1937, for a new business tax in 1951, for the fight against alcoholism in 1963 and for tax reform in 1974). Requests for complete revision are even less frequent: three attempts were unsuccessful (in 1851, 1866 and 2003), while the fourth was rejected by the people on 8 September, 1935.

A fourth type of initiative has existed for only a few years, but has never been used. When the Constitution was revised in 1999, a new form of initiative was defined, called the "general popular initiative", which allows "the adoption, modification or repeal of constitutional or legislative provisions", but only in the form of a proposal conceived in general terms. The aim of introducing this new type of popular initiative was to offer citizens the possibility of amending federal laws without having to go through a constitutional amendment. The initiative was created following the vote of 9 February, 2003; however, it was withdrawn on 27 September 2009, only six years after its creation, without having been used.

At the end of 2019, the municipality of Sion in southwestern Switzerland launched an experiment in participatory democracy, based on the model of the Citizens' Initiative Review already tested in the US state of Oregon. The main aim of this initiative was to encourage democratic debate. Twenty participants were randomly selected from Sion's electorate on the basis of gender, age, political orientation, level of education and history of electoral participation, to be representative of the population. This panel of 20 people met over two weekends to debate, inform themselves and exchange views with experts, supporters and opponents of a federal project to be put to the vote. At the end of their work, they produced a one-page report summarizing the issues, the main arguments for and against, and their conclusions. The aim was to explain the subject of the vote "in a comprehensible and complete manner, without falling into simplification", to "respond to the current crisis of democracy by involving citizens".