Public Citizen is an American non-profit consumer advocacy organization and progressive think tank founded in 1971 by consumer activist and lawyer Ralph Nader. It is dedicated to advancing consumer rights, government accountability, and corporate responsibility, with a focus on protecting public health, safety, and democracy. The organization employs litigation, lobbying, research, and public education to influence policy across all three branches of the U.S. federal government.

Its work spans a wide array of issues, including challenging unsafe drugs and medical practices, combating toxic exposures in workplaces, advocating for safer vehicles and consumer products, fighting voter suppression and political corruption, and holding energy companies accountable for exploitation. Through divisions such as the Health Research Group, the Energy Program, and the Congress Watch arm, it pursues public interest litigation and has achieved landmark legal actions and policy reforms that have reshaped regulations in areas like food safety, environmental protection, and financial oversight. The organization also publishes reports, testifies before Congress, and mobilizes public support to counter corporate influence.

Public Citizen was established partly to support fundraising for Nader's other initiatives, such as the Center for the Study of Responsive Law and the U.S. Public Interest Research Group, and has since grown into a prominent voice for consumer interests. Over its five decades, it has contributed to the creation of agencies like the Consumer Product Safety Commission and the Occupational Safety and Health Administration. It continues to monitor and critique government policies, with a particular emphasis on transparency, fair trade, and democratic integrity. The Public Citizen Foundation, a related entity, supports its non-lobbying activities such as education and litigation, ensuring the organization's impact resonates in both legal and public spheres.