Princeton Day School is a private coeducational day school located in Princeton, in Mercer County, in the U.S. state of New Jersey, serving students in pre-kindergarten through twelfth grade. The largest division is the Upper School (grades 9–12), with an enrollment of about 420. The school has been accredited by the Middle States Association of Colleges and Schools Commission on Elementary and Secondary Schools since 1989.

As of the 2023–24 school year, the school had an enrollment of 952 students (plus 20 in PreK) and 128.1 classroom teachers (on an FTE basis), for a student–teacher ratio of 7.4:1.

The school is a member of the National Association of Independent Schools, New Jersey Association of Independent Schools and the Association of Delaware Valley Independent Schools.