The Glass Fire was a wildfire in Northern California, that started on September 27, 2020, at 3:48 AM (PDT) from an undetermined cause and was active for 23 days. It was part of the 2020 California Wildfires and the 2020 Western United States wildfire season. The fire was named due to its origin nearby Glass Mountain Road in Deer Park, Napa County, and it extended also into Sonoma County. Initially a single 20-acre brush fire, it rapidly grew and merged with two smaller fires that expanded to 11,000 acres during the night of September 27 into September 28.

The 2020 California wildfire season, part of the 2020 Western United States wildfire season, was a record-setting year of wildfires in California. By the end of the year, 9,917 fires had burned 4,397,809 acres (1,779,730 ha), more than 4% of the state's roughly 100 million acres of land, making 2020 the largest wildfire season recorded in California's modern history, though roughly equivalent to the pre-1800 levels which averaged around 4.4 million acres yearly and up to 12 million in peak years. California's August Complex fire has been described as the first "gigafire", burning over 1 million acres across seven counties, an area larger than the state of Rhode Island. The fires destroyed over 10,000 structures and cost over $12.079 billion in damages, including over $10 billion in property damage and $2.079 billion in fire suppression costs. The intensity of the fire season has been attributed to a combination of more than a century of poor forest management and higher temperatures resulting from climate change.