Use these resources in OpenSecrets.org's Influence & Lobbying section, which are also found at the left, to learn more about Washington's influence industry and its most powerful players.

Just about any interest group you can think of has a presence in Washington-and spends money to maintain that presence. Here we've totaled all the campaign contributions over the years from more than 100 interest groups, so that you can see patterns that might have affected policies with an impact on your life. We also track how much interest groups have been spending on lobbying, which is the other side of the influence coin.

Professional advocates make big bucks to lobby members of Congress and government officials on the issues their clients care about. But the money that industries, companies, unions and issue groups spend on lobbying is often just a drop in the bucket compared to what they can reap in return if their lobbyists are successful. Here you can see who spends what on federal lobbying and where they focus their resources.

You've heard it before - it's not what you know, it's who you know. In our nation's capital, success comes with a combination of knowledge and personal connections. This database tracks thousands of individuals who've spun through Washington's "revolving door", employing professional relationships and know-how accumulated through public service to advance the goals of their private employers.

In a campaign finance system where all the money originates from individuals, political action committees, or PACs, control the most "corporate" of money. Controlled by companies, trade associations, unions, issue groups and even politicians (a subset called "leadership PACs"), these committees pool contributions from individuals and distribute them to candidates, political parties and other PACs. PACs can also spend money independently on political activities, including advertising and other efforts to support or oppose candidates in an election.

Influence in Washington is created from many ingredients. Here we give you at-a-glance profiles of the political donations, outside spending and lobbying expenditures of more than 20,000 labor unions, corporations and trade groups, as well as the number of lawmakers who have personally invested in them. More detailed profiles are available for the 150 or so biggest all-time contributors since 1989.

For the longest time, campaign ads were almost exclusively produced by candidates and political parties, but in recent years outside issue groups have been getting in on the action. They often operate as so-called 527 committees (taking their name from the relevant section of the IRS tax code). Sometimes mysteriously named, these advocacy groups frequently have ties to labor, big business and super-wealthy individuals. Unlike political committees, they can accept unlimited contributions from just about anyone, and they deploy that money in various ways to influence elections. Keep an eye on these shadowy groups here.