This chapter traces the recent rise of activist street bands in the United States (mainly brass, woodwinds, and percussion—loud, lively, and mobile), and places them in an historical context, with specific attention to how bands across the country are experimenting to achieve the greatest social impact. In 2006, organizers in Somerville, Massachusetts, created the first festival for the gathering of activist street bands under the polysemic term “HONK!” They noted that bands honk their horns for the same reasons motorists honk: “to arouse fellow travelers, to warn of danger, to celebrate milestones, and to just plain have fun.” In the ensuing years, HONK! festivals quickly emerged in Seattle, New York, Providence, Austin, and Detroit. Participating bands draw from many musical traditions, including New Orleans, Balkan, Brazilian, and pop. Band members, generally amateurs, learn music aurally and/or through written music, allowing for a wide level of ability, often inspiring onlookers to play. Some bands have leaders; many are leaderless. In the public and digital commons, activist street bands attract attention. This chapter asks probing questions about whether they have an impact. What are the lessons learned about how best to partner with nonprofit organizations, NGOs, or campaigns to convey the desired messages? What significance do gender, ethnicity, and class have in these partnerships?