The anarchist companionship is the relationship system of the anarchist movement in Western Europe and a part of the world from the end of the 19th century onwards, encompassing both formal and informal anarchist networks guided by shared values such as hospitality and financial or practical aid to fellow companions. These networks also engaged in supporting other social struggles of the period, even those that were not explicitly anarchist.

This transnational network, lacking a real nerve center or central authority, allowed anarchists of the time to meet, consult, and undertake joint actions while providing them with significant mobility across Europe. The companions shared a set of structuring elements that united them: common values, a shared commitment to the anarchist struggle, and a collective imaginary, particularly shaped by the anarchist press and songs of the period.

Born as a response to state repression in Europe, this shifting and decentralized network proved difficult for authorities to control. They portrayed it as the result of a vast international anarchist conspiracy and as a new Black International (1881–1887), an interpretation that does not reflect the reality of anarchist companionship. Attempts to suppress it generally failed due to its elusive nature.

After the Ère des attentats (1892–1894) and the growing distinction between individualist anarchists and anarcho-communists, anarchists turned to other forms of action and coordination, particularly anarcho-syndicalism. Although anarchist companionship evolved and took on new forms, strong markers remain, including the terms 'companion' or 'friend', making it an anarchist counterpart to the more communist-linked term of 'comrade'.

The term companion literally means 'bread fellow, messmate'. The term replaced citizen among anarchists in France in the early 1880s for several reasons, some of which were noted by the Boulangist newspaper La Cocarde in 1888:

A few words about this epithet companion, which anarchists use to refer to one another. Citizen was the republican word, I would even say the revolutionary one. But citizen implied a right of citizenship (civitas, civis), a contract agreed upon with a governing power: citizen suited only slaves, from an anarchist perspective. Something else had to be found. They created the term companion, which, in fact, carried no obligations.

During this period, companions were generally men, although women could also be part of the movement. Contrary to the view upheld in earlier historiography of the movement, companions were not necessarily young, celibate men. In the French Nord department, for instance, among male companions, 67% were between 20 and 35 years old, 27.7% were over 35, and only 4.8% were under 20, which presents the image of a movement primarily composed of militants in their 'age prime'. Moreover, police reports on companions indicate a relatively equal number of married and single men, without accounting for free unions or cohabitation, which also existed.

In France, a certain number of companions were foreigners, mainly Italians, Russians, Polish, Belgians, Spanish, or British people. However, sources on them are difficult to analyze, as they belonged to circles that were challenging for the French authorities to infiltrate, making precise details hard to determine. From a socio-economic perspective, companions were predominantly involved in manual work, but far from all of them were artisans. Additionally, their professions varied greatly depending on location, while one city might have a majority of artisans, another might have mostly factory workers, making the composition of the movement quite diverse.