Médecins Sans Frontières (MSF; pronounced [medsɛ̃ sɑ̃ fʁɔ̃tjɛʁ] (listen)), sometimes rendered in English as Doctors Without Borders, is an international humanitarian medical non-governmental organisation (NGO) of French origin best known for its projects in conflict zones and in countries affected by endemic diseases. Main areas of work include diabetes, drug-resistant infections, HIV/AIDS, hepatitis C, tropical and neglected diseases, tuberculosis, vaccines and COVID. They contribute to patents and intellectual property subjects, as well as research and development. In 2019, the group was active in 70 countries with over 35,000 personnel mostly local doctors, nurses and other medical professionals, logistical experts, water and sanitation engineers and administrators. Private donors provide about 90% of the organisation's funding, while corporate donations provide the rest, giving MSF an annual budget of approximately US$1.63 billion.Médecins Sans Frontières was founded in 1971, in the aftermath of the Biafran famine of the Nigerian Civil War, by a small group of French doctors and journalists who sought to expand accessibility to medical care across national boundaries and irrespective of race, religion, creed or political affiliation. To that end, the organisation emphasises "independence and impartiality", and explicitly precludes political, economic, or religious factors in its decision making. For these reasons, it limits the amount of funding received from governments or intergovernmental organisations. These principles have allowed MSF to speak freely with respect to acts of war, corruption, or other hindrances to medical care or human well-being. Only once in its history, during the 1994 genocide in Rwanda, has the organisation called for military intervention.

MSF's principles and operational guidelines are highlighted in its Charter, the Chantilly Principles, and the later La Mancha Agreement. Governance is addressed in Section 2 of the Rules portion of this final document. MSF has an associative structure, where operational decisions are made, largely independently, by the five operational centres (Amsterdam, Barcelona-Athens, Brussels, Geneva and Paris). Common policies on core issues are coordinated by the International Council, in which each of the 24 sections (national offices) is represented. The International Council meets in Geneva, Switzerland, where the International Office, which coordinates international activities common to the operational centres, is also based.

MSF has general consultative status with the United Nations Economic and Social Council. It received the 1999 Nobel Peace Prize in recognition of its members' continued efforts to provide medical care in acute crises, as well as raising international awareness of potential humanitarian disasters. James Orbinski, who was the president of the organization at the time, accepted the prize on behalf of MSF. Prior to this, MSF also received the 1996 Seoul Peace Prize. Christos Christou succeeded Joanne Liu as international president in June 2019.