A lobbyist is an activist usually paid by an interest group to promote their positions to legislatures. A lobbyist can also work to change public opinion through advertising campaigns or by influencing 'opinion leaders' or pundits, thereby creating a climate for the change his or her employer desires. The word lobbyist comes from the chambers in which the act of lobbying usually takes place, an anteroom near legislative bodies, for instance, or even the lobby of hotels where important people are staying. In American politics, most lobbyist organizations are headquartered on or near K Street in Washington DC, so "K Street" has become somewhat synonymous for lobbying. It is very easy for a lobbyist to stray into bribery -- the most direct way to influence legislation, obviously, is to bribe enough law makers to ensure that the bill you support passes. Therefore, lobbying is heavily regulated. Of course, a lobbyist rarely makes the news unless he or she has transgressed the regulations, and as a result, 'lobbyist' has rather negative connotations these days. Measures to control the influence of lobbyists include campaign finance reforms, often promised but rarely passed. When legislators lose re-election or choose not to run again for office, they often find a second career as a highly paid lobbyist, meeting with their former colleagues and touting the positions they are paid to promote. Of course, these are positions they supported while in office, so such jobs are not completely mercenary, yet they are widely considered an abuse of one's former position. This practice is, however, quite legal. Routinely, political scandals surface that have their roots in some lobbyist activity or other -- usually unlawfully large gifts to lawmakers, or quid pro quos of some form. From wiseGeek.

A lobbyist is an educator. Legislators need to vote on hundreds of pieces of legislation (bills) but don't have the time nor expertise to fully analyze all the details of every bill. Legislators rely on their staff to educate them, but also they rely on lobbyists to give them the "Reader's Digest" version of a bill. Lobbyists are hired by private companies, business entities, non-profit groups, local governmental entities, employee group associations and unions, and every type of professional organization under the sun to learn a particular client or clients' issues, then relay information to the legislators about how a bill will impact the client; positively or negatively. Most lobbyists are very dedicated to their clients AND to making sure that they provide honest answers and analysis to lawmakers. Most also are very ethical and follow the many laws established to insure that votes are made honestly and without undue influence. As with any business, a few bad guys cause all to be painted with broad stroke.