Groundhog Day (Pennsylvania German: Grund'sau dk, Grundsaudaag, Grundsow Dawg, Murmeltiertag; Nova Scotia: Daks Day) is a popular North American tradition observed in the United States and Canada on February 2. It derives from the Pennsylvania Dutch superstition that if a groundhog emerges from its burrow on this day and sees its shadow due to clear weather, it will retreat to its den, and winter will go on for six more weeks; if it does not see its shadow because of cloudiness, spring will arrive early.

While the tradition remains popular in the 21st century, studies have found no consistent association between a groundhog seeing its shadow and the subsequent arrival time of spring-like weather.The weather lore was brought from German-speaking areas where the badger (German: Dachs) is the forecasting animal. This appears to be an enhanced version of the lore that clear weather on the Christian festival of Candlemas forebodes a prolonged winter.

The Groundhog Day ceremony held at Punxsutawney in western Pennsylvania, centering on a semi-mythical groundhog named Punxsutawney Phil, has become the most frequently attended ceremony. Grundsow Lodges in Pennsylvania Dutch Country in the southeastern part of the state observe the occasion as well. Other cities in the United States and Canada also have adopted the event.

Punxsutawney (; Lenape: Punkwsutènay) is a borough in the south of Jefferson County, Pennsylvania, United States. Punxsutawney is known for its Groundhog Day celebration each February 2, during which thousands of attendees and international media outlets visit the town for an annual weather prediction by the groundhog Punxsutawney Phil.The borough, located 84 miles (135 km) northeast of Pittsburgh and 50 miles (80 km) northwest of Altoona, was incorporated in 1850. With a population of 5,962 as of the 2010 census, Punxsutawney is the largest incorporated municipality in Jefferson County.