Entryism (or entrism or enterism) is a political tactic by which an organisation encourages members to infiltrate another organisation in an attempt to gain recruits, or take over entirely.

In situations where the larger organization is hostile to entryism, the entryists may engage in a degree of subterfuge to hide the fact that they are, in fact, an organization in their own right. In the case of the Militant Tendency, this was done by claiming that the tendency was in fact simply a newspaper, Militant, its editorial board and readers. Militant was open about its support for Trotskyism and revolutionary socialism. Other entrist groups have gone to the extent of hiding their political views as well as their organisational existence.

An important thing to note is that entryism does not involve dissolving the small organisation into the larger one. Entryism is generally (but not always) done secretly and often in organisations run on democratic centralist lines. Entryism is a logical conclusion from Leninist political theory which postulates that a "revolutionary vanguard" can sucessfully forment a revolution within a larger capitalist society.

Entryism is not an exclusivly left-wing phenomenon; it is also found in the far-right entering mainstream right-wing groups. e.g. British National Party members joining the UK Independence Party.In the US the John Birch Society, and other groups were accused of entryism in relation to the surprise selection of Barry Goldwater as the Republican candidate for US President in the 1964 election.

Socialist Entryism

Entryism sui generis (Slow Entryism)

Many Entryists engage in a long-term perspective in which they work within an organization for decades in hopes of gaining influence and a degree of power and perhaps even control of the larger organization. This is sometimes known as entryism sui generis.

The former was attempted by the Militant Tendency in Britain who worked within the Labour Party from the 1960s on and managed to get a controlling influence in the Young Socialists and Liverpool Council before being expelled in the 1980s. Many other Trotskyist groups have attempted similar feats but failed to gain the influence Militant attained.

In France, Trotskyist organizations, most notably the Parti des Travailleurs, have successfully infiltrated trade unions and attempted to infiltrate mainstream left-wing parties. In Australia, the practice was widespread during the 1950s, where Communists battled against Catholics and other anti-Communists, known as 'Groupers', for control of Australian trade unions. The Groupers subsequently formed the breakaway Democratic Labor Party.

Trotsky's "French Turn" (Fast Entryism)

A "split perspective" is sometimes employed in which the smaller party intends to remain in the larger party for a short period of time with the intention of splitting the organization and leaving with more members than they began with. This is the classical version of entryism advocated by Leon Trotsky in his essays on "the French Turn" in which Trotskyists entered the youth wing of the French Socialist Party (the SFIO) for a brief period in the 1930s.

Open Entryism

Some political parties, such as the Workers' Party in Brazil or the Scottish Socialist Party allow political tendencies to openly organize within them. In these cases the term entryism is not usually used. Political groups which work within a larger organisation but also maintain a "public face" often reject the term "entryism" but are nevertheless usually considered to be entryists by the larger organisation.

Religious entryism

A similar technique is used by the Aryan Nations Religious branch Church of Jesus Christ-Christian / Christian Identity as well as the Creativity Movement in taking over small churches.

The Reform Party of the United States of America

During the 2000 presidential election in the United States, some members of the Reform Party, which had been founded by Ross Perot, charged that the presidential campaign of Pat Buchanan was engaging in entryism. However, while a large number of new members did join to support Buchanan, he did not maintain a large separate organization outside of the Reform Party. It is worth noting that, after the election, many of Buchanan's support did split from the Reform Party, taking several state organizations with them, to form the America First Party. Ironically, the America First Party itself was quickly engaged in a controversy involving alleged entryism by supporters of James "Bo" Gritz.

Another example of charges of entryism involving the United States Reform Party involved supporters of Fred Newman and the New Alliance Party joining the Reform Party en masse and gaining some level of control over the New York State affiliate of the Reform Party. Another United States politican, Lyndon LaRouche, has attempted an entryism strategy in the Democratic Party since 1980, but with little success.