Frederick is a city in and the county seat of Frederick County, Maryland, United States. It is part of the Washington–Baltimore combined statistical area. It is located at an important crossroads at the intersection of a major north–south Native American trail and east–west routes to the Chesapeake Bay, both at Baltimore and what became Washington, D.C. and across the Appalachian mountains to the Ohio River watershed. It is a part of the Washington-Arlington-Alexandria, DC-VA-MD-WV Metropolitan Statistical Area, which is part of a greater Washington-Baltimore-Arlington, DC-MD-VA-WV-PA Combined Statistical Area.

Frederick's population was 78,171 people as of the 2020 U.S. census, making it the second-largest incorporated city in Maryland behind Baltimore. Frederick is home to Frederick Municipal Airport (IATA: FDK), which accommodates general aviation, and Fort Detrick, a U.S. Army bioscience and communications research installation and Frederick County's largest employer.

Frederick's relative proximity to Washington, D.C., has always been an important factor in the development of its local economy, along with the presence of Fort Detrick, its largest employer. Frederick is the home of Riverside Research Park, a large biomedical research park located on Frederick's east side. Tenants include the relocated main offices of the National Cancer Institute's Frederick National Laboratory for Cancer Research as well as Charles River Labs. As a result of continued and enhanced federal government investment, the Frederick area will likely maintain a continued growth pattern over the next decade. Frederick has also been impacted by recent national trends centered on the gentrification of the downtown areas of cities across the nation (particularly in the northeast and mid-Atlantic), and to re-brand them as sites for cultural consumption.