A look at the type of groups raising money for elections and what information they are required to disclose:
Candidates: Federal, state and local candidates are required to disclose their contributors and campaign spending, but some states have looser reporting requirements and enforcement than others. Wisconsin no longer requires campaign donors to disclose their employers.
Political action committees: The committees, known as PACs, raise and spend money to elect or defeat candidates. They must follow certain contribution limits and must report their donors.
Super PACs: Super PACs can raise unlimited amounts of money from individuals, corporations, unions and associations, and spend unlimited amounts to advocate for or against political candidates. They are different from traditional PACs in that they can't donate money directly to political candidates and cannot coordinate with candidates. They must report their donors, but can accept money from groups that don't have disclosure requirements.
527s: These groups are tax-exempt organizations that raise money for political activities. Named for a section of the federal tax code, they are typically focused on influencing an issue, policy, appointment or election. They can raise unlimited amounts of money from individual donors as well as corporations and labor unions, but have to register with the IRS and disclose contributions and spending.
Tax-exempt nonprofit groups: There are several different types of groups organized under the 501(c) section of the federal tax code, none of which are required to disclose their donors. Some of them, known as 501(c)(3) groups, are organizations that aren't supposed to engage in any political activities. Others in this category are widely considered "dark money" groups because they can spend money on politics.
By the Milwaukee Journal Sentinel and The Sacramento Bee.