Unions may organize a particular section of skilled workers (craft unionism), a cross-section of workers from various trades (general unionism), or attempt to organize all workers within a particular industry (industrial unionism). The agreements negotiated by a union are binding on the rank and file members and the employer and in some cases on other non-member workers. Trade unions traditionally have a constitution which details the governance of their bargaining unit and also have governance at various levels of government depending on the industry that binds them legally to their negotiations and functioning.
Originating in Great Britain, trade unions became popular in many countries during the Industrial Revolution. Trade unions may be composed of individual workers, professionals, past workers, students, apprentices or the unemployed. Trade union density, or the percentage of workers belonging to a trade union, is highest in the Nordic countries.
Since the publication of the History of Trade Unionism (1894) by Sidney and Beatrice Webb, the predominant historical view is that a trade union "is a continuous association of wage earners for the purpose of maintaining or improving the conditions of their employment." Karl Marx described trade unions thus: "The value of labour-power constitutes the conscious and explicit foundation of the trade unions, whose importance for the working class can scarcely be overestimated. The trade unions aim at nothing less than to prevent the reduction of wages below the level that is traditionally maintained in the various branches of industry. That is to say, they wish to prevent the price of labour-power from falling below its value" (Capital V1, 1867, p. 1069).
A modern definition by the Australian Bureau of Statistics states that a trade union is "an organization consisting predominantly of employees, the principal activities of which include the negotiation of rates of pay and conditions of employment for its members."
Yet historian R.A. Leeson, in United we Stand (1971), said: