A trade union or labor union is an organization run by and for workers who have banded together to achieve common goals in key areas such as wages, hours, and working conditions. The trade union, through its leadership, bargains with the employer on behalf of union members (rank and file members) and negotiates labor contracts (Collective bargaining) with employers. This may include the negotiation of wages, work rules, complaint procedures, rules governing hiring, firing and promotion of workers, benefits, workplace safety and policies. The agreements negotiated by the union leaders are binding on the rank and file members and the employer and in some cases on other non-member workers.
These organizations may comprise individual workers, professionals, past workers, or the unemployed. The most common, but by no means only, purpose of these organizations is "maintaining or improving the conditions of their employment"
Over the last three hundred years, many trade unions have developed into a number of forms, influenced by differing political and economic regimes. The immediate objectives and activities of trade unions vary, but may include:
The origins of trade unions' existence can be traced from the eighteenth century, where the rapid expansion of industrial society drew women, children, rural workers, and immigrants to the work force in larger numbers and in new roles. This pool of unskilled and semi-skilled labor spontaneously organized in fits and starts throughout its beginnings, and would later be an important arena for the development of trade unions. Trade unions as such were endorsed by the Catholic Church towards the end of the 19th Century. Pope Leo XIII in his 'Magna Carta': Rerum Novarum, spoke against the atrocities workers faced and demanded that workers should be granted certain rights and safety regulations.
Trade unions have sometimes been seen as successors to the guilds of medieval Europe, though the relationship between the two is disputed. Medieval guilds existed to protect and enhance their members' livelihoods through controlling the instructional capital of artisanship and the progression of members from apprentice to craftsman, journeyman, and eventually to master and grandmaster of their craft. A labor union might include workers from only one trade or craft, or might combine several or all the workers in one company or industry.
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." 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:
Recent historical research by Bob James in Craft, Trade or Mystery (2001) puts forward the view that trade unions are part of a broader movement of benefit societies, which includes medieval guilds, Freemasons, Oddfellows, friendly societies, and other fraternal organizations.
As Smith noted, unions were illegal for many years in most countries (and Smith argued that schemes to fix wages or prices, by employees or employers, should be). There were severe penalties for attempting to organize unions, up to and including execution. Despite this, unions were formed and began to acquire political power, eventually resulting in a body of labor law that not only legalized organizing efforts, but codified the relationship between employers and those employees organized into unions. Even after the legitimization of trade unions there was opposition, as the case of the Tolpuddle Martyrs shows.
The right to join a trade union is mentioned in article 23, subsection 4 of the Universal Declaration of Human Rights (UDHR), which also states in article 20, subsection 2 that "No one may be compelled to belong to an association". Prohibiting a person from joining or forming a union, as well as forcing a person to do the same (e.g. "closed shops" or "union shops", see below), whether by a government or by a business, is generally considered a human rights abuse. Similar allegations can be leveled if an employer discriminates based on trade union membership. Attempts by an employer, often with the help of outside agencies, to prevent union membership amongst their staff is known as union busting.
The National Labor Union was the first national union in the United States. It was created in 1866 and included many types of workers. Although relatively short-lived, the NLU paved the way for future American unions. Following the decline of the NLU, the Knights of Labor became the leading countrywide union in the 1860s. This union did not include Chinese, and partially included black people and women.
The Knights of Labor was founded in the United States in 1869. They opposed child labor and demanded the eight-hour day. They hoped their union would give workers “a proper share of the wealth they create,” more free time, and generally more benefits. They also tried to set up companies owned by the workers themselves. Although the Knights were against strikes, some radical members went on strike anyway when the railroads cut wages in 1884. After they won the fight, membership in the Knights grew to 700,000, but then, at the time of the Haymarket Massacre, a fearful public opinion grouped them with anarchists and Communists, and membership then rapidly declined.
The American Federation of Labor (AFL) was founded by Samuel Gompers. By 1904, AFL-affiliated unions had a membership of over 1.4 million nationwide. Under Gompers's leadership, the AFL advocated an approach known as "business" or "pure and simple" unionism, which emphasized collective bargaining to reach its goals. Demands were centered around improvements to the immediate work environment, like better wages, hours and working conditions.
In France, Germany, and other European countries, socialist parties and democrats played a prominent role in forming and building up trade unions, especially from the 1870s onwards. This stood in contrast to the British experience, where moderate New Model Unions dominated the union movement from the mid-nineteenth century and where trade unionism was stronger than the political labor movement until the formation and growth of the Labour Party in the early years of the twentieth century.
Supporters of Unions, such as the ACTU or Australian Labor Party, often credit trade unions with leading the labor movement in the early 20th century, which generally sought to end child labor practices, improve worker safety, increase wages for both union workers, raise the entire society's standard of living, reduce the hours in a work week, provide public education for children, and bring other benefits to working class families. 
Union structures, politics, and legal status vary greatly from country to country. For specific country details see below.
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). These unions are often divided into "locals", and united in national federations. These federations themselves will affiliate with Internationals, such as the International Trade Union Confederation.
In many countries, a union may acquire the status of a "juristic person" (an artificial legal entity), with a mandate to negotiate with employers for the workers it represents. In such cases, unions have certain legal rights, most importantly the right to engage in collective bargaining with the employer (or employers) over wages, working hours, and other terms and conditions of employment. The inability of the parties to reach an agreement may lead to industrial action, culminating in either strike action or management lockout, or binding arbitration. In extreme cases, violent or illegal activities may develop around these events.
In other circumstances, unions may not have the legal right to represent workers, or the right may be in question. This lack of status can range from non-recognition of a union to political or criminal prosecution of union activists and members, with many cases of violence and deaths having been recorded both historically and contemporarily. 
Unions may also engage in broader political or social struggle. Social Unionism encompasses many unions that use their organizational strength to advocate for social policies and legislation favorable to their members or to workers in general. As well, unions in some countries are closely aligned with political parties.
Unions are also delineated by the service model and the organizing model. The service model union focuses more on maintaining worker rights, providing services, and resolving disputes. Alternately, the organizing model typically involves full-time union organizers, who work by building up confidence, strong networks, and leaders within the workforce; and confrontational campaigns involving large numbers of union members. Many unions are a blend of these two philosophies, and the definitions of the models themselves are still debated.
Although their political structure and autonomy varies widely, union leaderships are usually formed through democratic elections.
Some research, such as that conducted by the ACIRRT, argues that unionized workers enjoy better conditions and wages than those who are not unionized.
Companies that employ workers with a union generally operate on one of several models:
As labor law varies from country to country, so is the function of unions. For example, in Germany only open shops are legal; that is, all discrimination based on union membership is forbidden. This affects the function and services of the union. In addition, German unions have played a greater role in management decisions through participation in corporate boards and co-determination than have unions in the United States. (newsletter/files/BTS012EN_12-15.pdf}.
In Britain, a series of laws introduced during the 1980s by Margaret Thatcher's government restricted closed and union shops. All agreements requiring a worker to join a union are now illegal. In the United States, the Taft-Hartley Act of 1947 outlawed the closed shop, but permitted the union shop unless the state government chose to prohibit it.
In addition, unions' relations with political parties vary. In many countries unions are tightly bonded, or even share leadership, with a political party intended to represent the interests of working people. Typically this is a left-wing, socialist, or social democratic party, but many exceptions exist. In the United States, by contrast, although it is historically aligned with the Democratic Party, the labor movement is by no means monolithic on that point; this is especially true among the individual "rank and file" members. For example, the International Brotherhood of Teamsters has supported Republican Party candidates on a number of occasions and the Professional Air Traffic Controllers Organization (PATCO) endorsed Ronald Reagan in 1980. (However, when PATCO went on strike in violation of their "no strike" contract, President Reagan ordered them back to work. Those who didn't return to the job were fired and replaced, effectively destroying PATCO.) The AFL-CIO has been against liberalizing abortion, consistent with a Republican position, so as not to alienate its large Catholic constituency. In Britain the labor movement's relationship with the Labour Party is fraying as party leadership embarks on privatization plans at odds with what unions see as the worker's interests. On top of this in the past there as been a group known as the Conservative Trade Unionists or CTU. A group formed of people who sympathized with right wing Tory policy but were Trade Unionists.
In Western Europe, professional associations often carry out the functions of a trade union. In these cases, they may be negotiating for white-collar workers, such as physicians, engineers, or teachers. Typically such trade unions refrain from politics or pursue a more ordoliberal politics than their blue-collar counterparts .
In Germany the relation between individual employees and employers is considered to be asymmetrical. In consequence, many working conditions are not negotiable due to a strong legal protection of individuals. However, the German flavor or works legislation has as its main objective to create a balance of power between employees organized in unions and employers organized in employers associations. This allows much wider legal boundaries for collective bargaining, compared to the narrow boundaries for individual negotiations. As a condition to obtain the legal status of a trade union, employee associations need to prove that their leverage is strong enough to serve as a counterforce in negotiations with employers. If such an employees association is competing against another union, its leverage may be questioned by unions and then evaluated in a court trial. In Germany only very few professional associations obtained the right to negotiate salaries and working conditions for their members, notably the medical doctors association Marburger Bund and the pilots association Vereinigung Cockpit. The engineers association Verein Deutscher Ingenieure does not strive to act as a union, as it also represents the interests of engineering businesses.
Finally, the structure of employment laws affects unions' roles and how they carry out their business. In many western European countries wages and benefits are largely set by governmental action. The United States takes a more laissez-faire approach, setting some minimum standards but leaving most workers' wages and benefits to collective bargaining and market forces. Historically, the Republic of Korea has regulated collective bargaining by requiring employers to participate but collective bargaining has been legal only if held in sessions before the lunar new year. In totalitarian regimes such as Nazi Germany, Trade Unions were outlawed. In the Soviet Union and China, unions have typically been de facto government agencies devoted to smooth and efficient operation of government enterprises.
See main article: Opposition to trade unions.
Trade unions have been accused of benefiting the insider workers, those having secure jobs, at the cost of the outsider workers, consumers of the goods or services produced, and the shareholders of the unionized business. Those who are likely to be disadvantaged most from unionization are the unemployed, those at risk of unemployment, or workers who are unable to get the job they want in a particular line of work.
In the United States, the outsourcing of labor to Asia, Latin America, and Africa has been partially driven by increasing costs of union partnership, which gives other countries a comparative advantage in labor, making it more efficient to perform labor-intensive work there. Milton Friedman, Nobel economist an advocate of laissez-faire capitalism sought to show that unionization produces higher wages (for the union members) at the expense of fewer jobs, and that, if some industries are unionized while others are not, wages will tend to decline in non-unionized industries.Recent global financial struggles have often been linked to unions and the long term affect that they have on an economy. In some cases, unions are regarded as a form of legalized conspiracy and extortion. American racketeering statutes still include an exemption for union activity.
Trade unions have been said to have ineffective policies on racism and sexism, such that a union is justified in not supporting a member taking action against another member. This was demonstrated by the 1987 judgment in the Weaver v NATFEH case in the UK - in which a black Muslim woman brought a complaint of workplace racist harassment against a co-trade unionist. The finding was that in the event of the union offering assistance to the complainant it would be in violation of the union’s duty to protect the tenure of the accused member and the judgment still sets the precedent for cases of this kind that union members who make complaints to the employer of racist or sexist harassment against member(s) of the same union cannot obtain union advice or assistance; this applies irrespective of the merit of the complaint.
Unions are sometimes accused of holding society to ransom by taking strike actions that result in the disruption of public services.  Gallup carries out annual polls on US support for labor unions; the proportion approving of labor unions has remained between 55 and 65% since the early 1970s.
The largest organization of trade union members in the world is the Brussels-based International Trade Union Confederation, which today has approximately 309 affiliated organizations in 156 countries and territories, with a combined membership of 166 million. Other global trade union organizations include the World Federation of Trade Unions.
National and regional trade unions organizing in specific industry sectors or occupational groups also form global union federations, such as Union Network International, the International Federation of Journalists or the International Arts and Entertainment Alliance.
Another source of labor news is the Workers Independent News, a news organization providing radio articles to independent and syndicated radio shows.
Labor Notes is the largest circulation cross-union publication remaining in the United States. It reports news and analysis about labor activity or problems facing the labor movement.
. Edward L. Ayers. American Passages: A History of the United States. Vol. 1. Harcourt. 978-0-4950-5015-5. 288.