Science Olympiad, sometimes abbreviated as SciOly or SO, is an American team competition in which students compete in 23 events pertaining to various fields of science. The subjects include earth science, biology, chemistry, physics, and engineering. Over 7,800 middle school and high school teams from 50 U.S. states compete with each year. The U.S. territories do not compete. However, several international teams do compete in Science Olympiad tournaments in the U.S.

There are multiple levels of the competition: invitational, regional, state, and national. Invitational tournaments, usually run by high schools and universities, are unofficial tournaments and serve as practice for regional and state competitions. Teams that excel at regional competitions advance to the state level; the top one or two teams from each state (depending on the state) then advance the national level. Winners later receive several kinds of awards, including medals, trophies and plaques, as well as scholarships. The program for elementary-age students is less common and less consistent. Schools have flexibility to implement the program to meet their needs. Some communities host competitive elementary tournaments.

The first recorded Science Olympiad was held on Saturday, November 23, 1974, at St. Andrews Presbyterian College in Laurinburg, North Carolina. Dr. Barnes and Dr. David Wetmore were the originators of this event. Fifteen schools from North and South Carolina participated in this event. It was a day-long affair, with competitions and demonstrations for high school students in the areas of biology, chemistry, and physics. There were four event periods during this day and each event period had one fun event (like beaker race or paper airplane), one demonstration (like glassblowing and holography), and one serious event (like periodic table quiz or Science Bowl). An article by David Wetmore was published in the Journal of Chemical Education in January 1978 documenting the success of recruiting students through Science Olympiad. St. Andrews Presbyterian College continues to host a Science Olympiad tournament to this day. Mr. John C. "Jack" Cairns was a teacher at Dover High School in Delaware when he learned about the Science Olympiad tournament in North Carolina. He shared this information with Dr. Douglas R. Macbeth, the Delaware State Science Supervisor. Mr. Cairns was appointed to a steering committee to organize the first Science Olympiad in Delaware which took place at Delaware State University in the Spring of 1977. A write-up in The Science Teacher of December 1977 caught the attention of Gerard Putz, who proposed that the program be expanded throughout the United States. After competition tests in Michigan at the Lawrence Institute of Technology and Oakland University in 1983 and 1984, Putz and Delaware director John Cairns took their plan for a national competition to the National Science Teachers Conference in Boston. The first National Tournament was attended by representatives of 17 states, held at Michigan State University in 1985. Since then, the program has expanded greatly, with 60 teams present in each division at the National Tournament.

Since 2012, a Global Ambassador Team from Japan has been invited to attend the national tournament as part of a partnership between Science Olympiad, MEXT and JST. Each year, the Grand Prize for winning the Japan High School Science Championships (JHSSC), a competition styled after the U.S.-based Science Olympiad is a trip to the U.S. to participate in the Science Olympiad National Tournament. The Japanese Global Ambassador Team does however only compete on a limited basis as unranked guests. Japan continues to send a team, as of the 2025 National Tournament. The Japanese Global Ambassador Teams are the best known international teams that participate in Science Olympiad however other countries do occasionally participate in tournaments.

Canada has multiple active Science Olympiad teams and participated in the nationals tournaments in the U.S. between 1995 and 1998 but has not sent a team since although Canadian teams do still occasionally participate in tournaments in the U.S.

There are three divisions in the hierarchy of Science Olympiad:

The national tournament and generally state and regional tournaments are only for divisions B and C. Division A teams usually have separate interscholastic tournaments, apart from the more common intra-school competitions. Note that 6th and 9th graders have the option of competing in either of the two divisions in which they meet the grade requirements and are part of the competing school. (6th graders can compete in divisions A and B while 9th graders can compete in divisions B and C.) A middle school may, however, only use up to 2 members who have graduated to the next school if they are in 9th grade or lower. Students in grades lower than the division in which the school competes in may also be on the team. Teams are restricted to two 9th graders for division B and seven 12th graders for division C. Students may not participate on multiple teams, e.g. a 9th grader on both a high school and middle school team would not be allowed.

In Divisions A, B and C, teams may compete in up to twenty-three main events, which usually occur over a single day (some tournaments, such as the Texas State tournament, run competitive events over multiple days); done by a team of no more than 15 members. Events fall into five main categories: Life, Personal, and Social Science, Earth & Space Science, Physical Science & Chemistry, Technology & Engineering, Inquiry & Nature of Science. They are either knowledge-based (for example, written tests on earth science, physics, astronomy, or biology), hands-on (for example, chemistry lab practicals or events involving both device testing and an exam), or engineering-based (participants construct a device before the competition to do specified tasks on the day of the competition).