The United States National Chemistry Olympiad (or USNCO) is a contest held by the American Chemical Society (ACS) used to select the four-student team that represents the United States at the International Chemistry Olympiad (IChO).
Each local ACS section selects eight students (or more for larger ACS sections) to take the USNCO National Exam. To qualify for the national exam, students must first take the local exam. Approximately 16,000 U.S. students sit for the local exam each year. More than 1000 students qualify to take the National Exam annually.