In the United States and Canada, a political action committee (PAC) is a type of organization that pools campaign contributions from members and donates those funds to campaign for or against candidates, ballot initiatives, or legislation. The legal term PAC has been created in pursuit of campaign finance reform in the United States. This term is quite specific to all activities of campaign finance in the United States. Democracies of other countries use different terms for the units of campaign spending or spending on political competition (see political finance). At the U.S. federal level, an organization becomes a PAC when it receives or spends more than $1,000 for the purpose of influencing a federal election, and registers with the Federal Election Commission, according to the Federal Election Campaign Act as amended by the Bipartisan Campaign Reform Act of 2002 (also known as the McCain-Feingold Act). At the state level, an organization becomes a PAC according to the state's election laws.
Federal multi-candidate PACs may contribute to candidates as follows:
In its 2010 case Citizens United v. FEC, the Supreme Court of the United States overturned sections of the Campaign Reform Act of 2002 (also known as the McCain-Feingold Act) that had prohibited corporate and union political independent expenditures in political campaigns. Citizens United made it legal for corporations and unions to spend from their general treasuries to finance independent expenditures related to campaigns, but did not alter the prohibition on direct corporate or union contributions to federal campaigns. Organizations seeking to contribute directly to federal candidate campaigns must still rely on traditional PACs for that purpose.
Federal law formally allows for two types of PACs: connected and non-connected. Judicial decisions added a third classification, independent-expenditure only committees, which are colloquially known as "Super PACs".
Most of the 4,600 active, registered PACs are "connected PACs" established by businesses, labor unions, trade groups, or health organizations. These PACs receive and raise money from a "restricted class", generally consisting of managers and shareholders in the case of a corporation and members in the case of a union or other interest group. As of January 2009, there were 1,598 registered corporate PACs, 272 related to labor unions and 995 to trade organizations. 
Groups with an ideological mission, single-issue groups, and members of Congress and other political leaders may form "non-connected PACs". These organizations may accept funds from any individual, connected PAC, or organization. As of January 2009, there were 1,594 non-connected PACs, the fastest-growing category.
Elected officials and political parties cannot give more than the federal limit directly to candidates. However, they can set up a Leadership PAC that makes independent expenditures. Provided the expenditure is not coordinated with the other candidate, this type of spending is not limited.
Under the FEC (Federal Election Commission) rules, leadership PACs are non-connected PACs, and can accept donations from individuals and other PACs. Since current officeholders have an easier time attracting contributions, Leadership PACs are a way dominant parties can capture seats from other parties. A leadership PAC sponsored by an elected official cannot use funds to support that official's own campaign. However, it may fund travel, administrative expenses, consultants, polling, and other non-campaign expenses.
Between 2008 and 2009, leadership PACs raised and spent more than $47 million.
Super PACs, officially known as "independent-expenditure only committees", may not make contributions to candidate campaigns or parties, but may engage in unlimited political spending independently of the campaigns. Unlike traditional PACs, they can raise funds from individuals, corporations, unions, and other groups without any legal limit on donation size.
Super PACs were made possible by two judicial decisions: the aforementioned Citizens United v. Federal Election Commission and, two months later, Speechnow.org v. FEC. In Speechnow.org, the federal Court of Appeals for the D.C. Circuit held that PACs that did not make contributions to candidates, parties, or other PACs could accept unlimited contributions from individuals, unions, and corporations (both for profit and not-for-profit) for the purpose of making independent expenditures.
The result of the Citizens United and SpeechNow.org decisions was the rise of a new type of political action committee in 2010, popularly dubbed the "super PAC". In an open meeting on July 22, 2010, the FEC approved two Advisory Opinions to modify FEC policy in accordance with the legal decisions. These Advisory Opinions were issued in response to requests from two existing PACs, Club for Growth, and Commonsense Ten, which later became Senate Majority PAC. The opinions gave a sample wording letter which all Super PACs must submit to qualify for the deregulated status, and such letters continue to be used by Super PACs up to the present date. FEC Chairman Steven T. Walther dissented on both opinions and issued a statement giving his thoughts. In the statement, Walther stated "There are provisions of the Act and Commission regulations not addressed by the court in SpeechNow that continue to prohibit Commonsense Ten from soliciting or accepting contributions from political committees in excess of $5,000 annually or any contributions from corporations or labor organizations." (emphasis in original)
The term "Super PAC" was coined by reporter Eliza Newlin Carney. According to Politico, Carney, a staff writer covering lobbying and influence for CQ Roll Call, "made the first identifiable, published reference to 'super PAC' as it’s known today while working at National Journal, writing on June 26, 2010, of a group called Workers’ Voices, that it was a kind of '"super PAC" that could become increasingly popular in the post-Citizens United world.'"
According to FEC advisories, Super PACs are not allowed to coordinate directly with candidates or political parties. This restriction is intended to prevent them from operating campaigns that complement or parallel those of the candidates they support or engaging in negotiations that could result in quid pro quo bargaining between donors to the PAC and the candidate or officeholder. However, it is legal for candidates and Super PAC managers to discuss campaign strategy and tactics through the media.
Super PACs may support particular candidacies. In the 2012 presidential election, Super PACs played a major role, spending more than the candidates' election campaigns in the Republican primaries. As of early April 2012, Restore Our Future—a Super PAC usually described as having been created to help Mitt Romney's presidential campaign—had spent $40 million. Winning Our Future (a pro–Newt Gingrich group) spent $16 million. Some Super PACs are run or advised by a candidate's former staff or associates.
In the 2012 election campaign, most of the money given to super PACs came from wealthy individuals, not corporations. According to data from the Center for Responsive Politics, the top 100 individual super PAC donors in 2011–2012 made up just 3.7% of contributors, but accounted for more than 80% of the total money raised, while less than 0.5% of the money given to "the most active Super PACs" was donated by publicly traded corporations. Super PACs have been criticized for relying heavily on negative ads.
As of February 2012, according to Center for Responsive Politics, 313 groups organized as Super PACs had received $98,650,993 and spent $46,191,479. This means early in the 2012 election cycle, PACs had already greatly exceeded total receipts of 2008. The leading Super PAC on its own raised more money than the combined total spent by the top 9 PACS in the 2008 cycle.
The 2012 figures do not include funds raised by state level PACs.
By January 2010, at least 38 states and the federal government required disclosure for all or some independent expenditures or electioneering communications. These disclosures were intended to deter potentially or seemingly corrupting donations.
Yet despite disclosure rules, it is possible to spend money without voters knowing the identities of donors before the election. In federal elections, for example, political action committees have the option to choose to file reports on a "monthly" or "quarterly" basis. This allows funds raised by PACs in the final days of the election to be spent and votes cast before the report is due.
In one high-profile case, a donor to a super PAC kept his name hidden by using an LLC formed for the purpose of hiding their personal name. One super PAC, that originally listed a $250,000 donation from an LLC that no one could find, led to a subsequent filing where the previously "secret donors" were revealed. However, campaign finance experts have argued that this tactic is already illegal, since it would constitute a contribution in the name of another.
In the 2008 election, the top nine PACs spent a total of $25,794,807 (directly, and via their affiliates and subsidiaries) as follows: