A union is an organization of workers who act together to secure benefits and rights in the workplace. Unionism is an important tool for worker's rights, and many trade unions are open to membership all over the world. Members of a union may range from machinists in auto-repair shops to in home care providers who belong to a service-workers union. Not all workers are unionized, but many are, especially when they work for large companies. Many unions are also quite powerful, since they represent thousands of employees, and unions have traditionally played a role in politics as well, by endorsing union-friendly candidates.

The first unions began to emerge in the 18th century, as industrialization began to rise in Europe. Some historians believe that these unions are related to trade guilds, medieval organizations which originally protected specialized trades such as weaving, bread baking, and building. Others feel that unions are not, in fact, related to guilds, and that they arose as a natural response to changing workplaces.

Members of a union pay dues to support the activities of the union and they also elect leaders and stewards. These people are responsible for representing the collective interests of the union when the union negotiates with a company owner or employer. Stewards usually work on the ground, ensuring that union members are not being exploited and that the terms of their contracts are being met, while representatives bring issues to the bargaining table during negotiations.

Union bargaining typically results in set policies about employee benefits, working hours, and other issues of importance. In a workplace where non-unionized employees work alongside unionized ones, some of these agreements may cover non-unionized workers as well. The union will also represent the needs of individual employees, helping to arbitrate when an employee has a dispute about wages, working hours, and similar issues with his or her employer. In some cases, a union may hold a strike or another type of labor action to gain the upper hand in negotiations.

Some well known trade unions include the Industrial Workers of the World (IWW), Knights of Labor, the Service Employees Union International (SEIU), and the American Federation of Labor-Congress of Industrial Organizations (AFL-CIO). Typically, when someone commences employment at a unionized company, he or she will be offered union membership. In other cases, employees may choose to unionize their workplaces in the hopes of negotiating better working conditions.