The 2012 campaign cycle marks the first presidential election since the 2010 Supreme Court ruling that allowed corporations and unions to spend more freely in federal elections. The loosened campaign finance rules, coupled with an intense competition between the two major parties, have served only to embolden independent political groups that hope to influence the 2012 races.

Below is a list of most major groups that have been active or expect to be active in the 2012 federal elections. Many of these groups can accept unlimited donations. Others can accept unlimited donations and avoid disclosing their donors. There’s even a new breed of so-called independent groups that advocate solely for a single presidential candidate.

Who are these groups and who’s behind them? Click on the links below to find out.

The groups below were selected based on the amount they have spent, or say they plan to spend, or the media attention they have attracted. It is not a comprehensive list, and additional groups will be added as the campaign season unfolds.