One of the deep insights of anarchist theory is that means and ends are inseparable. The method of struggle will have important repercussions on the realisable ends. The development of Anarchist theory and practice has been a search for liberatory methods that are likely to create the society that we hope to see. The role of the organisation then has to fall in line with those tactics and strategies that are liable to bring about a libertarian society.
"The Organisational Platform of the Libertarian Communists"  (Abbreviated: The Platform) was first written after the failure of the revolution in Russia and the Ukraine. An attempt was made to give solutions to those factors in the struggle which had lead to failure.
In 1936, a syndicalist revolution was attempted in Spain. This attempt also failed. The Friends of Durutti Group  formed in 1937 in an attempt to guard the ideological purity of anarchism, and to advocate against the regimentation of the military. This initiative however, came too late, after the argument had already been lost.
Again, starting in 1956, we see the emergence of the FAU , also in rough agreement with the guidelines given by the Platform though likely developed quite independently. Later we see the FARJ  express a slightly more nuanced understanding of how the anarchist organisation should function in relation to the mass movement. This understanding was born out of the practice in working with various social groups, including the unions and students.
None of these initiatives were ultimately successful. However, the notion of Platformism, the Anarchist Vanguard group   and Especifismo  have seen growing interest in recent years. This interest grows out of repeated failure by anarchists to gain traction since the failed revolution of '36 and a look at the (qualified) successes of the Especifismo approach.
In order to have a libertarian revolution, the manner in which the power of the state is dispensed with is essential. The "seizure of the state", as Leninist groups approach the problem, simply replaces one form of rule with another. In order to change the structures of power fundamentally, from the base, it is necessary to have a social revolution.
Specifism is an hypothesis. One which has not fully been tested or seen unqualified success. This hypothesis however is rooted in experience, of both success and failure, gained in real struggles. Since the working class is at such a disadvantage, we have not seen any unqualified successes, and therefore those techniques that look promising must be evaluated with a combination of theoretical probing and active attempts at implementation.
The hypothesis is that anarchists should organise into specific political organisations with the intention of promoting the development and radicalisation of elements in those sectors of society which can represent the interests of the working class. These sectors might include the unions, students, unemployed, community groups or anywhere else that strategic and tactical analysis would point towards as a promising sector.
This interaction with particular sectors, which we will call social engagement* involves the active participation of militants in these mass organisations and sectors in ways that will advance the class. The basic rule of thumb for determining advancement is summed up in the following maxim "anarchists should actively promote the increasing participation and power of the working class". That is, we would like to see self-actualisation, self-organisation and the building of prefigurative libertarian structures. This rule of thumb, however, is insufficient. We must attempt to express the libertarian worldview simultaneously. This can happen in the ideological vacuum that is a consequence of struggle, when the illegitimacy of the common sense notions that we inherit from capitalist society are exposed. We need to be bold in widening the division in thinking as the working class begin to see the bankruptcy of ruling class ideas.
Towards Non-Substitutive Engagement
Political revolution is the revolution of heroes, the revolution of a minority. Social revolution is the revolution of the common people, a revolution of the great masses. - Liu Shifu
Social engagement is an alternative to both the substitutionism of Lenin and Guevara, and its tacit rejection so often characterised by those who define themselves in opposition to Leninism in the anarchist milieu and the ultra-left. While not all Leninist or Guevarist tactics are substitutive, they tend to have no critique of the practice. If the revolutionary vanguard, the active or militant classes or the guerrilla armies substitute themselves for the working class then there is no libertarian revolution.
This is true because the elements who substitute can not know the aims of the working class. In the subjective sense, this class can't even be said to exist in the absence of the realisation of their own position in society. In the absence of their own consciousness of existence, they can't have any collective sense of needs. Their needs would then have to be assessed by a group that did not include them, but was outside them. Liberty is about the capacity to make choices. Any revolution in which decisions are made in ones stead, or on ones behalf, is not libertarian.
Neither can this substitutive element increase working class participation by acting in its stead. This participation is a crucial ingredient towards the creation of a new society run by the working class, for the working class. A substitutive group will eventually develop its own class interests.
History has born out this lesson with impressive regularity including the great "communist" revolutions of Russia and China. In the end, both Russia and China devolved into oligarchic capitalism as the substituted revolutionaries relaxed naturally into their position as the new ruling class.
The negation of the Leninist programme, which was first embraced by the ultra-left and later by many groups including the Forest-Johnson tendency, and various anarchist and other libertarian communist groups, is now widely accepted in the libertarian left.
This negation views Leninism's direct active participation in struggle as so dangerous that any sort of activity is in danger of being substitutive. Interaction bears a threat of infection. In this atmosphere most libertarian groups have become either closed or interact only through propaganda, attempting to enlighten the class, but not to guide them.
Social engagement however asks for a third path; interaction for the realisable gain of libertarian advantage. This means that anarchists would actively take part in organisations and communities attempting to build class power. They would argue in their unions for progressive politics and revolutionary goals. Pushing beyond arguments for improved conditions towards the complete removal of capitalism. They would argue in their schools for open access to education. They would argue in their communities to for common ownership of resources and services. All of this would be done by including and assisting cooperatively with the class.
* This has sometimes been called Social Insertion by South American comrades
 The Organisational Platform of the Libertarian Communists, Dielo Truda (Workers' Cause)
 The Manifesto of Libertarian Communism, Georges Fontenis
 The Friends of Durutti Group: 1937-1939, Agustin Guillamón
 Especifismo, NEFAC
 Interview with the Rio de Janeiro Anarchist Federation (FARJ)
 The FAU's Huerta Grande