Since industrial capitalism began, workers reacted to their conditions by combining to resist the bosses. As Marx wrote, “Combination always has a double aim, that of stopping competition among the workers, so that they can carry on general competition with the capitalist.” Unions are the first line of defense for workers and a means to increase their sense of solidarity, but because they fight the effects of the system rather than the system itself, unions also produce a layer of officials who, by dint of habit, become concerned more with the survival of the institution than the defense of the workers, and, in order to preserve the union, tend toward a preference for negotiation over conflict. This talk will discuss the importance, but also the limits, of unions, and what role socialists can play in them to make them better collective fighting organizations of the working class.