The Association of Community Organizations for Reform Now (ACORN) is a community-based organization that advocates for low- and moderate-income families by working on neighborhood safety, voter registration, health care, affordable housing, and other social issues. They, along with a number of other community unions, are affiliated under ACORN International.

In the US, ACORN was composed of a number of legally distinct nonprofit entities and affiliates including a nationwide umbrella organization established as a 501(c)(4) that performed lobbying; local chapters established as 501(c)(3) nonpartisan charities; and the national nonprofit and nonstock organization, ACORN Housing Corporation. ACORN's priorities included: better housing and wages for the poor, more community development investment from banks and governments, better public schools, labor-oriented causes and social justice issues. ACORN pursued these goals through demonstrations, negotiation, lobbying for legislation, and voter participation.

Unlike in the US, ACORN groups in other countries have little organizational funding. Under the ACORN model, most members are volunteers. Employed union organizers come from those working in local ACORN campaigns rather than from existing organizations and are paid a low wage. The union works on local and national level campaigns.

Founded in 1970 by Wade Rathke and Gary Delgado, at its peak ACORN had over 500,000 members and more than 1,200 neighborhood chapters in over 100 cities across the U.S. In 2002, ACORN International was created to aid the spread of ACORN's model to other countries. There are currently ACORN affiliates in Cameroon, Canada, Czech Republic, England, France, Honduras, India, Ireland, Italy, Kenya, Peru, Scotland, Tunisia, United States, and Wales.

ACORN suffered a damaging nationwide controversy in the fall of 2009 after James O'Keefe and Hannah Giles secretly made, edited and released videos of interactions with low-level ACORN personnel in several of their offices, leading to several investigations by state officials that concluded the videos were inaccurately portraying the personnel as encouraging criminal behavior. The organization didn't recover from the negative publicity in the US and dissolved, with ACORN members and organizers forming new organizations such as the Alliance of Californians for Community Empowerment (ACCE) Action. ACORN groups outside of the US continued unaffected. ACORN, under ACORN International, still works within the US through its Home Savers Campaign, for example.

ACORN investigated complaints against companies accused of predatory lending practices. ACORN also worked to support strict state laws against predatory practices, organized against foreclosure rescue scams, and steered borrowers toward loan counseling; Following a three-year campaign, Household International (now owned by HSBC Holdings and renamed HSBC Finance Corporation), one of the largest subprime lenders in the country, and ACORN announced on November 25, 2003, a proposed settlement of a 2002 national class-action lawsuit brought by ACORN. The settlement created a $72 million foreclosure avoidance program to provide relief to household borrowers who were at risk of losing their homes. The settlement came on the heels of an earlier $484 million settlement between Household, Attorneys General, and bank regulators from all 50 U.S. states.

Since the 1980s, ACORN conducted large-scale voter registration drives, focusing primarily on registering poor and minority citizens.

In 2001, ACORN opposed the privatization of some New York City schools, favoring its own Charter School plan.