Dogfish Head Brewery is a brewing company based in Milton, Delaware, United States, founded by Sam and Mariah Calagione and, as of 2019, owned by the Boston Beer Company. It opened in 1995 and produces 262,000 barrels of beer annually.

Select brews (including many of the brewery's seasonal and one-off selections) can be found in 31 U.S. states, plus Washington, D.C. Dogfish Head also licenses "Dogfish Head Alehouse" located in Gaithersburg, Maryland. Beer-paired food and vintage bottles of Dogfish Head's seasonal beers are available at their alehouses, as well as kegged offerings of their staple beers. The company also has a restaurant called Dogfish Head Brewings & Eats along with a seafood restaurant called Chesapeake & Maine that only sources seafood from the eponymous locations. Both are located in Rehoboth Beach, Delaware. In July 2014 the Dogfish Head Inn was established in Lewes, Delaware running along the Rehoboth-Lewes Canal.

The brewery was featured prominently in the documentary Beer Wars and was the subject of the Discovery Channel series Brew Masters, which premiered Sunday, November 21, 2010. The brewery takes its name from Dogfish Head, Maine, where Calagione spent summers as a child.

Sam Calagione started brewing in his kitchen in New York City, where he created his first beer out of overripe cherries with his roommates Ken Marino and Joe Lo Truglio. Dogfish Head has brew houses in Rehoboth, Lewes, and Milton, Delaware. The first successful beer that Dogfish Head produced was Midas Touch, which was brewed with honey, white Muscat grapes, and saffron. Although it started by only selling beer in the state of Delaware, Dogfish Head became one of the most profitable microbreweries in the United States. As of 2017 it distributed its beer in 38 states, the most recent being Louisiana.

Calagione sources ingredients from around the world. Dogfish Head has become one of the most watched and well-respected breweries in the country thanks in large part to Calagione's unconventional brewing methods. These ingredients made it possible for his company to grow. The company used to be the smallest microbrewery in the United States, with Calagoione starting with three very small kegs with propane burners beneath them. Dogfish Head's brewery in Rehoboth, Delaware, originally produced only 10 gallons of beer per day when it opened in June 1995. By 2018, Dogfish Head had become one of America's largest and most well-known breweries, producing around 15,000 gallons of beer per day.

In 2019, Calagione had informal talks with Jim Koch, co-founder of the Samuel Adams brewing Boston Beer Company, at the annual Extreme Beer Fest in Boston. Within a few months, they were purchased by Boston Beer Co. Dogfish Head announced the acquisition by the Boston Beer Company for $300 million on May 9, 2019. As part of the merger, Calagione and his wife, Mariah, converted their Dogfish Head stock into Boston Beer Co. stock, thereby becoming the second largest non-institutional owners of the merged companies.

Dogfish Head tends to produce experimental or "extreme" beers, such as the tongue-in-cheek "Liquor de Malt", a bottle-conditioned malt liquor, which typically comes in a Dogfish Head brown paper bag. Dogfish Head products often use non-standard ingredients, such as green raisins in Raison D'Être ale. Some beers, including the WorldWide Stout, 120 Minute India Pale Ale, and the raspberry-flavored strong ale Fort, are highly alcoholic, reaching 18% to 20% alcohol by volume (typical beers have around 3% to 7% alcohol by volume).^{[citation needed]}

One of Dogfish Head's more notable odd beers was a green beer called Verdi Verdi Good, produced in 2005 and sold only on draft. The beer was not colored green artificially; rather, the green color was derived from brewing a Dortmunder style beer that contained spirulina, or blue-green algae.