A parliamentary group, parliamentary caucus or political group is a group consisting of members of different political parties or independent politicians with similar ideologies. Some parliamentary systems allow smaller political parties, who are not numerous enough to form parliamentary groups in their own names, to join with other parties or independent politicians in order to benefit from rights or privileges that are only accorded to formally recognized groups. An electoral alliance, where political parties associate only for elections, is similar to a parliamentary group. A technical group is similar to a parliamentary group but with members of differing ideologies. In contrast, a political faction is a subgroup within a political party and a coalition forms only after elections.

Parliamentary groups may elect a parliamentary leader; such leaders are often important political players. Parliamentary groups in some cases use party discipline to control the votes of their members.

Parliamentary groups correspond to "caucuses" in the United States Congress and the Parliament of Canada. A parliamentary group is sometimes called the parliamentary wing of a party, as distinct from its organizational wing. Equivalent terms are used in different countries, including: Argentina (bloque and interbloque), Australia (party room); Austria (Klub); Belgium (fractie/fraction/Fraktion); Brazil and Portugal ("grupo parlamentar" or, informally, "bancadas"); Germany (Fraktion); Italy (gruppo), Finland (eduskuntaryhmä/riksdagsgrupp); the Netherlands (fractie); Poland (klub), Switzerland (fraction/Fraktion/frazione); Romania (grup parlamentar); and Russia (фракция/fraktsiya), Spain ('grupo parlamentario'), and Ukraine (фракція/fraktsiya). In some countries, there is a special category for groupings who do not full fill the criteria for a group: Germany (Parlamentarische Gruppe); Italy (componente), and Poland (koło).

Generally, parliamentary groups have some independence from the wider party organisations. It is often thought improper for elected MPs to take instructions solely from non-elected party officials or from the small subset of the electorate represented by party members. In any case, the exigencies of government, the need to cooperate with other members of the legislature and the desire to retain the support of the electorate as a whole often preclude strict adherence to the wider party's wishes. The exact relationship between the parliamentary party and the party varies between countries, and also from party to party. For example, in some parties, the parliamentary and organisational leadership will be held by the same person or people, whether ex officio or not; other parties maintain a sharp distinction between the two offices. Nevertheless, in almost all cases, the parliamentary leader is the public face of the party, and wields considerable influence within the organisational wing, whether or not they hold any official position there.

A parliamentary group is typically led by a parliamentary group leader or chairperson, though some parliamentary groups have two or more co-leaders. If the parliamentary group is represented in the legislature, the leader is almost always chosen from among the sitting members; if the leader does not yet have a seat in the legislature, a sitting member of the group may be expected to resign to make way for him or her. If the party is not represented in the legislature for the time being, the leader will often be put forward at a general election as the party's candidate for their most winnable seat. In some parties, the leader is elected solely by the members of the parliamentary group; in others, some or all members of the wider party participate in the election. Parliamentary groups often have one or more whips, whose role is to support the leadership by enforcing party discipline.

In Armenia, political parties often form parliamentary groups before running in elections. Prior to the 2021 Armenian parliamentary elections, four different parliamentary groups were formed. A parliamentary group must pass the 7% electoral threshold in order to gain representation in the National Assembly.

Higher electoral thresholds for parliamentary groups discourages the formation of parliamentary groups running in elections.

The parliamentary groups of the European Parliament must consist of no less than 25 MEPs from seven different EU member states. No party discipline is required. Parliamentary groups gain financial support and can join committees.