Petrified Forest National Park is an American national park in Navajo and Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about 346 square miles (900 square kilometers), encompassing semi-desert shrub steppe as well as highly eroded and colorful badlands. The park's headquarters is about 26 miles (42 km) east of Holbrook along Interstate 40 (I-40), which parallels the BNSF Railway's Southern Transcon, the Puerco River, and historic U.S. Route 66, all crossing the park roughly east–west. The site, the northern part of which extends into the Painted Desert, was declared a national monument in 1906 and a national park in 1962. The park received 644,922 recreational visitors in 2018.

Averaging about 5,400 feet (1,600 m) in elevation, the park has a dry windy climate with temperatures that vary from summer highs of about 100 °F (38 °C) to winter lows well below freezing. More than 400 species of plants, dominated by grasses such as bunchgrass, blue grama, and sacaton, are found in the park. Fauna include larger animals such as pronghorns, coyotes, and bobcats, many smaller animals, such as deer mice, snakes, lizards, seven kinds of amphibians, and more than 200 species of birds, some of which are permanent residents and many of which are migratory. About one third of the park is designated wilderness—50,260 acres (79 sq mi; 203 km²).

The Petrified Forest is known for its fossils, especially fallen trees that lived in the Late Triassic Epoch, about 225 million years ago. The sediments containing the fossil logs are part of the widespread and colorful Chinle Formation, from which the Painted Desert gets its name. Beginning about 60 million years ago, the Colorado Plateau, of which the park is part, was pushed upward by tectonic forces and exposed to increased erosion. All of the park's rock layers above the Chinle, except geologically recent ones found in parts of the park, have been removed by wind and water. In addition to petrified logs, fossils found in the park have included Late Triassic ferns, cycads, ginkgoes, and many other plants as well as fauna including giant reptiles called phytosaurs, large amphibians, and early dinosaurs. Paleontologists have been unearthing and studying the park's fossils since the early 20th century.

The park's earliest human inhabitants arrived 13,000 years ago. These Clovis-era people are the ancestors of Native Americans. By about 2,500 years ago Ancestral Pueblo farmers were growing corn and living in subterranean pit houses in what would become the park. By one-thousand years ago Ancestral Pueblo farmers lived in above-ground, masonry dwellings called pueblos and gathered in large communal buildings called great kivas. By AD 1450 Ancestral Pueblo farmers in the Petrified Forest migrated to join rapidly growing communities on the Hopi Mesas to the northwest and the Pueblo of Zuni to the east–these locations are still home to thousands of descendant community members today. More than 1000 archeological sites, including petroglyphs, have been discovered in the park. These ancestral places remain important to descendant communities. In the 16th century, Spanish explorers visited the area, and by the mid-19th century a U.S. team had surveyed an east–west route through the area where the park is now located and noted the petrified wood. Later, roads and a railway followed similar routes and gave rise to tourism and, before the park was protected, to large-scale removal of fossils. Theft of petrified wood remains a problem in the 21st century.