The Regeneron International Science and Engineering Fair (ISEF) is an annual science fair in the United States. It is owned and administered by the Society for Science, a 501(c)(3) non-profit organization based in Washington, D.C. Each May, more than 1800 students from roughly 75 countries and territories compete in the fair for scholarships, tuition grants, internships, scientific field trips and the grand prizes, including one $75,000 and two $50,000 college scholarships. All prizes together amount to over $8,000,000. Two major awards ceremonies are the Special Awards Organization Presentation and the Grand Awards Ceremony. The International Science and Engineering Fair was founded in 1950 by Science Service and was sponsored by Intel from 1997 to 2019. Regeneron Pharmaceuticals became the title sponsor for ISEF in 2020, but the event was cancelled that year and replaced with an online version due to the COVID-19 pandemic. The 2021 ISEF was a fully virtual event while 2022 was held online and in-person in Atlanta, GA, and 2023 was in person in Dallas, TX. The 2024 ISEF will be held in person in Los Angeles, CA.

A science fair or engineering fair is an event hosted by a school that offers students the opportunity to experience the practices of science and engineering for themselves. In the United States, the Next Generation Science Standards makes experiencing the practices of science and engineering one of the three pillars of science education. Students perform some sort of research and then present their experiment in a poster session or other display format.