In political science, the terms radical right, reactionary right, populist right, and hard right have been used to refer to the range of nationalist, right-wing and far-right political parties that have grown in support in Europe since the late 1970s. Populist right groups have shared a number of causes, which typically include opposition to globalisation and immigration, criticism of multiculturalism, and opposition to the European Union, with some opposing liberal democracy or rejecting democracy altogether in favor of "Illiberal democracy" or outright authoritarian dictatorship.

The ideological spectrum of the radical right extends from staunchly right-wing national conservatism and right-wing populism to far-right Third Positionism and other neo-fascist ideologies.

The Friedrich Ebert Foundation, in a 2011 book, defines the terms "right-wing extremist" and "right-wing populist" differently.

In 1996, the Dutch political scientist Cas Mudde noted that in most European countries, the terms "radical right" and "extreme right" were used interchangeably. He cited Germany as an exception, noting that among political scientists in that nation, the term "radical right" (Rechsradikalismus) was used in reference to those right-wing groups which were outside the political mainstream but which did not threaten "the free democratic order"; the term was thus used in contrast to the "extreme right" (Rechsextremen), which referred to groups which did threaten the constitutionality of the state and could therefore be banned under German law. According to the German scientist Klaus Wahl [de] "the radical right can be scaled by using different degrees of militancy and aggressiveness from right-wing populism to racism, terrorism, and totalitarianism".

The term "radical right" originated in U.S. political discourse, where it was applied to various anti-communist groups which were active in the 1950s era of McCarthyism. The term and accompanying concept then entered Western Europe through the social sciences. Conversely, the term "right-wing extremism" developed among European scholars, particularly those in Germany, to describe right-wing groups that developed in the decades following the Second World War, such as the West German National Democratic Party and the French Poujadists. This term then came to be adopted by some scholars in the U.S.

"The rise of new parties on the right in the 1980s led to a great deal of controversy over how these parties are defined. Some authors argue that these parties share essential characteristics, while others point to the unique national features and circumstances of each party. Some see them as throwbacks to the fascist era, while others see them as mixing right-wing, liberal, and populist platforms to broaden their electoral appeal. The party ideologues themselves have argued that they cannot be placed on the left-to-right spectrum."

In his study of the movement in Europe, David Art defined the term "radical right" as referring to "a specific type of far right party that began to emerge in the late 1970s"; as Art used it, "far right" was "an umbrella term for any political party, voluntary association, or extra-parliamentary movement that differentiates itself from the mainstream right". Most commentators have agreed that these varied radical right parties have a number of common characteristics. Givens stated that the two characteristics shared by these radical rights groups were:

In 2000, Minkenberg characterised the "radical right" as "a political ideology, the core element of which is a myth of a homogeneous nation, a romantic and populist ultranationalism which is directed against the concept of liberal and pluralistic democracy and its underlying principles of individualism and universalism. The contemporary radical right does not want to return to pre-democratic regimes such as monarchy or feudalism. It wants government by the people, but in terms of ethnocracy instead of democracy." In 2020, Wahl summarized that "ideologies of the radical right emphasize social and economic threats in the modern and postmodern world (e.g., globalization, immigration). The radical right also promises protection against such threats by an emphatic ethnic construction of 'we', the people, as a familiar, homogeneous in-group, anti-modern, or reactionary structures of family, society, an authoritarian state, nationalism, the discrimination, or exclusion of immigrants and other minorities ... While favoring traditional social and cultural structures (traditional family and gender roles, religion, etc.) the radical right uses modern technologies and does not ascribe to a specific economic policy; some parties tend toward a liberal, free-market policy, and others more to a welfare state policy."