National Nurses United (NNU) is the largest union and professional association of registered nurses in the United States, representing over 225,000 members across all 50 states. Founded in 2009 through the merger of the California Nurses Association/National Nurses Organizing Committee (CNA/NNOC), the United American Nurses (UAN), and the Massachusetts Nurses Association (MNA), NNU emerged as a response to the health care industry's assaults on patient care standards and nurses' working conditions. The organization is affiliated with the AFL-CIO and operates as a progressive voice for direct-care registered nurses (RNs), advocating for healthcare workers' rights, patient safety, safe staffing ratios, progressive economic policies, and the expansion of Medicare for All as a single-payer health care system to ensure quality care as a human right. NNU's affiliates include state nursing associations such as the New York State Nurses Association, which joined in 2022, and it has a history of successful organizing efforts, including recent unionizations at hospitals like Ascension Saint Agnes in Baltimore and St. Joseph Health in Texas.

NNU's core mission is to amplify the voices of RNs and patients in national and state policy arenas, challenging profit-driven health care structures that prioritize corporate interests over people. The union advocates for legislation enforcing safe nurse-to-patient ratios, as demonstrated by its pivotal role in defeating California Governor Arnold Schwarzenegger's 2004 attempt to roll back such laws. Additionally, NNU has established initiatives like the Registered Nurse Response Network (RNRN) in 2005, which provides disaster relief and humanitarian aid to affected communities worldwide, including responses to hurricanes in the U.S., earthquakes in Haiti, and typhoons in the Philippines. The organization also engages in political activism, such as condemning U.S. military actions abroad and supporting progressive economic policies, while negotiating some of the strongest collective bargaining contracts for RNs in the nation.

With roots tracing back over 120 years through its predecessor organizations, particularly CNA founded in 1903, NNU continues to build nurse power by organizing new chapters and fostering alliances with patients, consumers, and labor groups. It operates from a framework of patient-centered advocacy adopted in 1993, when direct-care RNs gained majority control of CNA's board. Despite its growth, NNU has faced adversarial relationships, such as coordinated efforts against corporate entities like the Blackstone Group, highlighting its role in broader networks of influence within health care and labor movements.