Politicisation (also politicization; see English spelling differences) is a concept in political science and theory used to explain how ideas, entities or collections of facts are given a political tone or character, and are consequently assigned to the ideas and strategies of a particular group or party, thus becoming the subject of contestation. Politicisation has been described as compromising objectivity, and is linked with political polarisation. Conversely, it can have a democratising effect and enhance political choice, and has been shown to improve the responsiveness of supranational institutions such as the European Union. The politicisation of a group is more likely to occur when justifications for political violence are considered acceptable within a society, or in the absence of norms condemning violence.

Depoliticisation, the reverse process, is when issues are no longer the subject of political contestation. It is characterised by governance through consensus-building and pragmatic compromise. It occurs when subjects are left to experts, such as technocratic or bureaucratic institutions, or left to individuals and free markets, through liberalisation or deregulation. It is often connected with multi-level governance. The concept has been used to explain the "democratic gap" between politicians and citizens who lack choice, agency and opportunities for deliberation. In the 21st century, depoliticisation has been linked to disillusionment with neoliberalism. Depoliticisation has negative consequences for regime legitimacy, and produces anti-political sentiment associated with populism, which can result in "repoliticisation" (politicisation following depoliticisation).

Current studies of politicisation are separated into various subfields. It is primarily examined on three separate levels: within national political systems, within the European Union and within international institutions. Academic approaches vary greatly and are frequently disconnected. It has been studied from subdisciplines such as comparative politics, political sociology, European studies and legal theory.

The politicisation of science occurs when actors stress the inherent uncertainty of scientific method to challenge scientific consensus, undermining the positive impact of science on political debate by causing citizens to dismiss scientific evidence.

The dominant academic framework for understanding politicisation is the systems model, which sees politics as an arena or sphere. In this perspective, politicisation is the process by which issues or phenomena enter the sphere of "the political", a space of controversy and conflict. Alternatively, in the behaviouralist approach to political science, which sees politics as action or conflict, politicisation is conceptualised as the process by which an issue or phenomenon becomes significantly more visible in the collective consciousness, causing political mobilisation.

In the systems model, depoliticisation is seen as "arena-shifting": removing issues from the political sphere by placing them outside the direct control or influence of political institutions, such as legislatures and elected politicians, thereby denying or minimising their political nature. In the behaviouralist model, depoliticisation indicates the reduction of popular interest in an issue, a weakening of participation in the public sphere and the utilisation of power to prevent opposition.

Majoritarian institutions, such as parliaments (legislatures) and political parties, are associated with politicisation because they represent popular sovereignty and their agents are subject to short-term political considerations, particularly the need to compete for votes ("vote-seeking") by utilising populist rhetoric and policies. Non-majoritarian institutions, such as constitutional courts, central banks and international organisations, are neither directly elected nor directly managed by elected officials, and are connected with depoliticisation as they tend towards moderation and compromise.

Declines in voter turnout, political mobilisation and political party membership, trends present in most OECD countries from the 1960s onwards, reflect depoliticisation. A number of causes for this shift have been suggested. The growth of big tent political parties (parties which aim to appeal to a broad spectrum of voters) resulted in reduced polarisation and centralised decision-making, with increased compromise and bargaining. In postwar Europe, the development of neo-corporatism led to political bargaining between powerful employers' organisations, trade unions and the government in a system known as tripartism, within which cartel parties could successfully prevent competition from newer parties. Globally during the late 20th century, central banks and constitutional courts became increasingly important.