In situations where the organisation being "entered" is hostile to entryism, the entryists may engage in a degree of subterfuge to hide the fact that they are, in fact, an organisation 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 entryist groups have gone to the extent of hiding both their political views and their organisational existence.
Entryism does not involve dissolving the small organisation into the larger one. Entryism is often (but not always) done secretly and often in organisations run on democratic centralist lines. Entryism is seen by some as a logical conclusion from Leninist political theory which postulates that a "revolutionary vanguard" can successfully foment a revolution within a larger capitalist society, but according to some, the strategy of entryism is as old as politics itself.
Proponents of the tactic advocated that the Trotskyists should enter the social democratic parties to connect with revolutionary socialist currents within them, and steer those currents toward Leninism. However, entry lasted only for a brief period: the leadership of the SFIO started to expel the Trotskyists. The Trotskyists of Workers Party of the United States also successfully used their entry into the Socialist Party of America to recruit their youth group and other members. Similar tactics were also used by Trotskyist organisations in other countries, including The Netherlands, Belgium, Switzerland and Poland. Entrism was used to connect with and recruit leftward moving political currents inside radical parties.
Since the turn in France, Marxists have used the tactic even if they had different preconceptions of how long the period of entry would last.
In 'entryism sui generis' (of a special type), Trotskyists, for example, do not openly argue for the building of a Trotskyist party. 'Deep entryism' refers to the long duration.
The tactic is closely identified with Michel Pablo and Gerry Healy, who were leaders of the Fourth International in the late 1940s and 1950s. The 'deep entry' tactic was developed as a way for Trotskyists to respond to the Cold War. In countries where there were mass social democratic or communist parties, it was as difficult to be accepted into these parties as Trotskyist currents as to build separate Trotskyist parties. Therefore Trotskyists were advised to enter secretly, and not to come forward as Trotskyists with their full program.
In Europe, this was the approach used, for example, by The Club in the Labour Party, and by Fourth Internationalists inside the Communist Parties. In France, Trotskyist organizations, most notably the Parti des Travailleurs, have successfully entered Communist-led trade unions and mainstream left-wing parties (see Lionel Jospin for a famous example).
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 politician, Lyndon LaRouche, has attempted an entryist strategy in the Democratic Party since 1980, but with little success.
The two major parties regularly complain of entryism tactics by the other - however complaints by the Democrats against Republicans are more common, leading to the term 'dirty tricks' being associated with the right wing since the Nixon Era. In 2007 the Republicans settled a lawsuit in New Hampshire with the Democrats after accusation of infiltration. In addition, Republican and Libertarian Party chapters have complained of takeover by religious or police elements, in one case in Colorado leading to scandal when the charges led to police department shake-ups.
Also, complaints of entryism among non-party activist groups have appeared in many chat groups.
Orchard had made his name as a leading opponent of free trade, which was perhaps the singular signature policy of the Progressive Conservative government of Brian Mulroney in the late 1980s and early 1990s. While opponents pointed to this remarkable distance, Orchard and his supporters argued that they represented "traditional" Tory values and economic nationalism that the older Conservative Party, and the Progressive Conservative party before Mulroney, had espoused, namely that of John Diefenbaker.
Opponents of the 2003 merger between the Progressive Conservative and Canadian Alliance parties also charged Alliance members with entryism. It was widely speculated that most, if not all of the approximately 25,000 Canadians who swelled the PC Party's membership before the merger vote were Alliance members. They would likely have voted in favour of the merger.
Members of Socialist Action, a small Trotskyist group, play a leading role in the New Democratic Party Socialist Caucus, a small faction on the left wing of that social democratic party, and advocate that their members join and engage with the NDP.
After the fall of Social Credit in British Columbia, the British Columbia Liberal Party saw the shift of former Social Credit members into the BC Liberal party. As a result, the new membership saw the party shift much more towards the right on fiscal policy. In this way, entryism led to a complete takeover of the original party by former Social Credit members. As a result of the more right wing policies of the British Columbia Liberal Party, the party is now officially separate from its federal counterpart, the Liberal Party of Canada.
New Zealand's Christian Right also attempted to obtain electoral influence. While the Coalition of Concerned Citizens infiltrated the National Party shortly before the 1987 general election, it met with little success. As a result of this abortive gesture, National quietly centralised its candidate selection procedures.