The Lawrenceville School is a private, coeducational preparatory school for boarding and day students located in the unincorporated community of Lawrenceville within Lawrence Township in Mercer County, in the U.S. state of New Jersey. Lawrenceville is a member of the Eight Schools Association and the Ten Schools Admission Organization.

As of the 2023–24 school year, the school had an enrollment of 802 students and 107.8 classroom teachers (on an FTE basis), for a student–teacher ratio of 7.4:1.

The Lawrenceville School was founded in 1810 as the Maidenhead Academy by Presbyterian clergyman Isaac Van Arsdale Brown. One of the oldest preparatory schools in the United States, it has had several names, including Lawrenceville Classical and Commercial High School and Lawrenceville Academy.

In 1883, the John Cleve Green Foundation purchased the school from its aging headmaster Samuel Hamill and renamed it The Lawrenceville School. Green, who had died in 1875, was born in the village of Lawrenceville and was one of Maidenhead Academy's original students. A merchant who amassed a large fortune investing in railroads, importing tea and textiles, and exporting opium to China. With no surviving children, much of his estate went to charitable causes.

The trustees of the Green Foundation, including Green's widow Sarah, brother Caleb, nephew Charles, and friend John T. Nixon, aimed to turn Lawrenceville into a college-preparatory institution "with a more elite student body." With $1.25 million to spend (approximately $40 million in 2024 dollars), they hired Presbyterian minister James Cameron Mackenzie to study the public schools of the United Kingdom, and later appointed him Head of School. Mackenzie's British-inspired innovations included Lawrenceville's house system, "the [first] small-unit housing plan ... in America." He argued that a "home-like atmosphere was better for an adolescent boy and made him a better student." Upon his return to the United States, the trustees commissioned a new campus from Frederick Law Olmsted and Peabody and Stearns, which has since been designated a U.S. National Historic Landmark District.

The 1883 reorganization of Lawrenceville successfully elevated the school's entire profile and turned it into nearby Princeton University's most reliable feeder school. Princeton president James McCosh had been searching for a Mid-Atlantic alternative to New England boarding schools, which he thought funneled their best students to New England schools such as Harvard. He used John Cleve Green's fortune to fill this gap. Green had been one of Princeton's most important donors; his great-great-great-grandfather Jonathan Dickinson had founded Princeton in 1746. Accordingly, the new Lawrenceville School was established "for the express purpose of preparing students for Princeton."

Lawrenceville was a large success; the school sent 20 students to Princeton in 1886 alone, and enrollment leaped from 112 students in 1883 to 362 by 1898. The relaunch marked the start of a large boom in the American boarding school industry.

In the 1940s, the school was considered by members of the American upper classes to be "very sophisticated and very cosmopolitan."