HONK! is a grassroots, non-profit event centered on resistance. Dancing groups and bands from all over the world come together to parade and play, protesting various social injustices, celebrating what they love, making a lot of noise, and having fun. HONK! is organized by an egalitarian committee that is always looking for help and ideas.

The festival was first organized in 2006 by the members of the Second Line Social Aid & Pleasure Society Brass Band of Somerville. The bands vary in style from New Orleans second line brass bands, European Klezmer, Balkan and Romani music, to Brazilian Afro Bloc and Frevo traditions, all embodying the passion and spirit of Mardi Gras and Carnival. Bands range in size from under ten to over thirty, all sharing a lot of horns and the capacity to HONK! The festival's motto, "Reclaiming the streets for horns bikes and feet" conveys its main message that public space belongs to the people. This message is reflected in some of the band names from 2008: Leftist Marching Brigade, Environmental Encroachment and the Rude Mechanical Orchestra. These "street bands" are just that, marchers dedicated to loud visibility and reclaiming public space. No bands are paid to participate in the festival and local residents feed and house all visiting performers. In fact, most of the HONK! budget is dedicated to financially helping bands participate in the festival.

Bands start playing on Saturday, performing in parking lots, streets, and the Plaza around Davis Square. On Sunday, bands, dancers, and community troupes meet in Davis Square to begin the parade, travelling through Davis Square, onto Massachusetts Avenue, and ending in Harvard Square. The parade is over 600 people long and thousands of spectators line the streets. Most groups have elaborate homemade costumes featuring floats, banners, or stilt walkers, all to catch people's attention. The evening of the parade, there is a HONK-off, or gathering of the bands, which has taken place at different places around Davis Square.