In politics, lobbying, persuasion, interest representation, government relations, or government affairs and sometimes legislative relations, legislative affairs, or advocacy, is the act of lawfully attempting to influence the actions, policies, or decisions of government officials, most often legislators or members of regulatory agencies, but also judges of the judiciary. Lobbying, which usually involves direct, face-to-face contact in cooperation with support staff that may not meet directly face-to-face, is done by many types of people, associations and organized groups, including individuals on a personal level in their capacity as private citizens, it is also practiced by corporations in the private sector serving their own interests, by non-profits and non-governmental organizations in the voluntary sector, by fellow legislators or government officials influencing each other through legislative affairs (legislative assistance) in the public sector, and by advocacy groups (interest groups). It is also an industry known by many of the aforementioned names, and has a near complete overlap with the public affairs industry. Lobbyists may be among a legislator's constituencies, for example amateur lobbyists such as a voter or a bloc of voters within their electoral district acting as private citizens; while others like professional lobbyists may engage in lobbying as a business or profession. Professional lobbyists are people whose business is trying to influence legislation, regulation, or other government decisions, actions, or policies on behalf of a group or individual who hires them. Individuals and nonprofit organizations can also lobby as an act of volunteering or as a small part of their normal job. Governments often define "lobbying" for legal purposes, and regulate organized group lobbying that has become influential.

The ethics and morals involved with legally bribing or lobbying or influence peddling are controversial. Lobbying can, at times, be spoken of with contempt, when the implication is that people with inordinate socioeconomic power are corrupting the law in order to serve their own interests. When people who have a duty to act on behalf of others, such as elected officials with a duty to serve their constituents' interests or more broadly the public good, can benefit by shaping the law to serve the interests of some private parties, a conflict of interest exists. Many critiques of lobbying point to the potential for conflicts of interest to lead to agent misdirection or the intentional failure of an agent with a duty to serve an employer, client, or constituent to perform those duties. The failure of government officials to serve the public interest as a consequence of lobbying by special interests who provide benefits to the official is an example of agent misdirection. That is why lobbying is seen as one of the causes of a democratic deficit.