The Washington International School (abbreviated as WIS; Spanish: Colegio Internacional de Washington; French: École Internationale de Washington) is a private international school in Washington, DC.

Established in 1966, WIS was the first school in the Washington area to offer the International Baccalaureate (IB) program.

The school has two campuses: the primary school (grades PK–5) in Georgetown, and the middle and upper school (grades 6–12) in Cleveland Park. The middle and upper school campus is located on the grounds of Marjorie Merriweather Post's Tregaron Estate.

The Washington International School's upper school was ranked as the 73rd most challenging high school in the country and the most challenging high school in the Washington, D.C., area by the Washington Post's "Ranking America's most challenging high schools" article in 2016. Popular school ranking website Niche listed it as the eighth best private high school in the D.C. area.

Washington International School (WIS) was founded in 1966 to serve the international community in the D.C. area. During the post-World War II era, many international schools were founded by a particular community or nationality and were "international" in the sense that students from other nationalities were accepted. From the very beginning, founder Dorothy Goodman envisioned that the school would educate children to become global citizens and the early curriculum reflected her vision. Children were taught several different languages and about world cultures, literature and history. In 1969, with assistance from the Ford Foundation, WIS expanded its campus with the purchase of the former Wendell Phillips School, which had closed a number of years before. In 1980 the Tregaron country house and estate was purchased and has been the site of the Middle (grades 6–8) and Upper Schools (9–12) ever since. The Elementary School moved out of the former Wendell Phillips School building in 1998 and the property was sold and developed into private housing. In the early 2000s, WIS constructed an “arts, academics, and athletics building” (AAA) containing a gymnasium, choral and band practice rooms, and classrooms. In 2021, the School launched a campaign to raise $30 million with the primary goal of constructing a new science centric facility on campus. It is scheduled to be completed in spring 2025.