Begun in 1998, this U.S.-based program provides opportunities for teachers to learn about and contribute to particle physics experiments and share what they learn with their students. This collaboration has yielded a variety of online instructional resources including raw datasets and derivative activities that provide opportunities for high school students to increase their understanding of particle physics and develop stronger scientific habits of mind. Teachers take part in: workshops at Fermilab (in Batavia, Illinois, U.S.), research appointments and mentoring at research institutions near their homes, peer discussion forums, classroom coaching visits by QuarkNet staff teachers, online activities with datasets and more. Teachers and students explore online data through e-Lab studies, the summer Boot Camp investigation, and masterclass exercises. Students with a QuarkNet cosmic ray muon detector upload data to an international data portal and analyze it in the Cosmic Ray e-Lab. QuarkNet centers are located throughout the U.S. to reach the widest audience. Typically, over 500 teachers participate each year. For full details, see the program overview sheet. QuarkNet receives support from the U.S. National Science Foundation, the U.S. Department of Energy, as well as Fermilab, ATLAS and CMS. Centers also receive in-kind contributions from their host institutions, and some have leveraged funds from other sources.