A grassroots movement (often referenced in the context of a political movement) as defined by Webster's Third International Dictionary, is one which uses the people in a given district as the basis for a political or economic movement. Grassroots movements and organizations utilize collective action from the local level to affect change at the local, regional, national, or international level. Grassroots movements are associated with bottom-up, rather than top-down decision making, and are sometimes considered more natural or spontaneous than more traditional power structures.  Grassroots movements utilize a variety of strategies from fundraising and registering voters, to simply encouraging political conversation. Goals of specific movements vary, but the movements are consistent in their focus on increasing mass participation in politics.
The idea of grassroots is often conflated with participatory democracy. The Port Huron Statement, a manifesto seeking a more democratic society, says that to create a more equitable society, "the grass roots of American Society" need to be the basis of civil rights and economic reform movements.  The terms can be distinguished in that grassroots often refers to a specific movement or organization, whereas participatory democracy refers to the larger system of governance. 
Movement in politics and activism
Grassroots movements use tactics that build power from local and community movements. Grassroots Campaigns, a non-profit organization dedicated to creating and supporting grassroots movements in America says that grassroots movements aim to raise money, build organizations, raise awareness, build name recognition, to win campaigns, and to deepen political participation. Grassroots movements work toward these and other goals via strategies focusing on local participation in either local or national politics.
Grassroots organizations derive their power from the people, thus their strategies seek to engage ordinary people in political discourse to the greatest extent possible. Below is a list of strategies considered to be grassroots because of their focus on engaging the populous. 
- Hosting house meetings or parties
- Having larger meetings—AGMs
- Putting up posters
- Talking with pedestrians on the street or walking door-to-door (often involving informational clipboards)
- Gathering signatures for petitions
- Mobilizing letter-writing, phone-calling, and emailing campaigns
- Setting up information tables
- Raising money from many small donors for political advertising or campaigns
- Organizing large demonstrations
- Asking individuals to submit opinions to media outlets and government officials
- Holding get out the vote activities, which include the practices of reminding people to vote and transporting them to polling places.
- Using online social networks to organize virtual communities
The earliest origins of the use of "grass roots" as a political metaphor are obscure. In the United States, an early use of the phrase "grassroots and boots" was thought to have been coined by Senator Albert Jeremiah Beveridge of Indiana, who said of the Progressive Party in 1912, "This party has come from the grass roots. It has grown from the soil of people's hard necessities".
In a 1907 newspaper article about Ed Perry, vice-chairman of the Oklahoma state committee, the phrase was used as follows: "In regard to his political views Mr. Perry has issued the following terse platform: 'I am for a square deal, grass root representation, for keeping close to the people, against ring rule and for fair treatment.'" A 1904 news article on a campaign for possible Theodore Roosevelt running mate Eli Torrance quotes a Kansas political organizer as saying: "Roosevelt and Torrance clubs will be organized in every locality. We will begin at the grass roots".
Since the early 1900s, grassroots movements have been widespread both in the United States and in other countries. Major examples include parts of the American Civil Rights Movement of the 1950s and 1960s, Brazils land equity movement of the 1970s and beyond, the Chinese rural democracy movement of the 1980s, and the German peace movement of the 1980s.
A particular instantiation of grassroots politics in the American Civil Rights Movement was the 1951 case of William Van Til working on integration of the Nashville Public Schools. Van Til worked to create a grassroots movement focused on discussing race relations at the local level. To that end, he founded the Nashville Community Relations Conference, which brought together leadership from various communities in Nashville to discuss the possibility of integration. In response to his attempts to network with leadership in the black community, residents of Nashville responded with violence and scare tactics. However, Van Til was still able to bring blacks and whites together to discuss the potential for changing race relations, and he was ultimately instrumental in integrating the Peabody College of Education in Nashville. Furthermore, the desegregation plan proposed by Van Til's Conference was implemented by Nashville schools in 1957. This movement is characterized as grassroots because it focused on changing a norm at the local level using local power. Van Til worked with local organizations to foster political dialogue, and was ultimately successful.
The Brazilian Landless Workers Movement (MST) was founded in the 1970s and has grown into an international organization. The MST focused on organizing young farmers and their children in fighting for a variety of rights, most notably the right to access land. The movement sought organic leaders, and used strategies of direct action such as land occupations. It largely maintained autonomy from the Brazilian government. The MST traces its roots to discontent arising from large land inequalities in Brazil in the 1960s. Such discontent gained traction, particularly after Brazil became a democracy in 1985. The movement focused especially on occupying land that was considered unproductive, thus showing that it was seeking overall social benefit. In the 1990s the influence of the MST grew tremendously following two mass killings of protestors. Successful protests were marked by the families of those occupying properties receiving plots of land. It is worth noting that although the grassroots efforts of the MST were successful in Brazil, when they were tried by the South African Landless People's Movement (LPM) in 2001 they were not nearly as successful. Land occupations in South Africa were politically contentious and did not achieve the positive results seen by the MST.
The National People's Congress was a grassroots democratic reform movement that came out of the existing Chinese government in 1987. It encouraged grassroots elections in villages all around China with the express purpose of bringing democracy to the local level of government. Reforms took the form of self-governing village committees that were elected in a competitive, democratic process. Xu Wang from Princeton University called the Congress mutually empowering for the state and the peasantry in that the state was given a renewed level of legitimacy by the democratic reforms, and the peasantry was given far more political power. This manifested itself in increased voting rate, particularly for the poor, and increased levels of political awareness according Wang's research. One example of the increased accountability from the new institutions was a province in which villagers gave 99,000 suggestions to the local government. Ultimately, 78,000 of which were adopted indicating a high rate of governmental responsiveness. This movement is considered grassroots because it focuses on systematically empowering the people. This focus manifested itself in the democratic institutions that focused on engaging the poor and in reform efforts that sought to make the government more responsive to the will of the people.
Another instance of a historical grassroots movement was the 1980s German peace movement. The movement traces its roots to the 1950s movement opposing nuclear armament, or the "Ban the Bomb" Movement. In the 1980s, the movement became far bigger. In 1981, 800 organizations pushed the government to reduce the military size. The push culminated in a protest by 300,000 people in the German capital Bonn. The movement was successful in producing a grassroots organization, the Coordination Committee, which directed the efforts of the peace movements in the following years. The committee ultimately failed to decrease the size of the German military, but it laid the groundwork for protests of the Iraq war in the 2000s. Further, the movement started public dialogue about policy directed at peace and security. Like the Civil Rights movement, the German Peace movement is considered grassroots because it focused political change starting at the local level. 
A further example of grassroots in the 1980s was the Citizens Clearinghouse for Natural Waste, an organization that united communities and various grassroots groups in America in support of more environmentally friendly methods of dealing with natural waste. The movement focused especially on African American communities and other minorities. It sought to bring awareness to those communities, and alter the focus from moving problematic waste to changing the system that produced such waste. The movement is considered grassroots because it utilized strategies that derived their power from the affected communities. For example, in North Carolina, African American communities lay down in from of dump trucks to protest their environment impact. The success of these movements largely remains to be seen.
Astroturfing refers to political action that is meant to appear to be grassroots, that is spontaneous and local, but in fact comes from an outside organization, such as a corporation or think tank.  It is named after AstroTurf, the iconic brand of artificial grass. Astroturfing means pretending to be a grassroots movement, when in reality the agenda and strategy are controlled by a hidden, non-grassroots organization. In this manner, a faux show is presented, consisting of robotic individuals pretending to be voicing their own opinions. An example of astroturfing was the ExxonMobil Corporation's push to create think tanks to disseminate false information about climate change. ExxonMobil was largely successful both in disseminating the information and in disguising the true nature of the think tanks.
More controversial examples of astroturfing often exhibit some characteristics of a real grassroots organization, but also characteristics of astroturf. Many of President Obama's efforts, for example, have been deemed grassroots because of their focus on involving the electorate at large. Critics of Obama have argued that some of these methods are in fact astroturfing because they believe that Obama faked the grassroots support. For example, the Reason Foundation has accused Obama of planting astroturf supporters in town hall meetings. Many movements and organizations must be placed on a continuum between grassroots and astroturf instead of labeled entirely as one or the other. For example, Australia's Convoy of No Confidence, a movement seeking to force an early election in 2011, incorporated elements of grassroots infrastructure in its reliance on the anger and discontentment of the participants. It also had elements of astroturf, namely the large extent to which it relied on support from political elites in the opposition party. 
The Tea Party, a conservative force in American politics that began in 2010, is also a controversial example of astroturfing. Democrats, notably President Barack Obama and Former Speaker of the House Nancy Pelosi, have accused the Tea Party of Astroturfing. They say that the movement purports to represent large swaths of America when in reality it comes a select few billionaires seeking policies favorable to themselves. The Tea Party has defended itself, arguing that it comes out of broad popular support and widespread anger at the Democratic Party and disenchantment with the GOP. Defenders of the Tea Party cite polls that find substantial support, indicating that the movement has some basis in grassroots politics. Critics point to the corporate influence on the Tea Party, which they believe indicates that the movement is more top-down than the grassroots rhetoric would suggest. The Tea Party can be considered grassroots to the extent that it comes from the people, but it is considered astroturfing to the extent that it is shaped by corporations and particularly wealthy individuals. 
Use in sport
The term "grassroots" is used by a number of sporting organizational bodies to reference the lowest, most elementary form of the game that anyone can play. Focusing on the grassroots of a sporting code can lead to greater participation numbers, greater support of professional teams/athletes and ultimately provide performance and financial benefits to the organization to invest into the growth and development of the sport. Some examples of this are FIFA's Grassroots Programme and the Football Federation Australia's "Goals for Grassroots" initiative.
- Abahlali baseMjondolo in South Africa
- Axis of Justice in USA
- Bhumi Uchhed Pratirodh Committee in India
- EZLN in Mexico
- Fanmi Lavalas in Haiti
- GlobalGiving — international
- Homeless Workers' Movement in Brazil
- Landless Peoples Movement in South Africa
- Landless Workers' Movement in Brazil
- Movement for Justice en el Barrio in USA
- Narmada Bachao Andolan in India
- Western Cape Anti-Eviction Campaign in South Africa
- Grassroots Campaigns a self-styled grassroots organization that works on elections in the USA. Recently, Grassroots Campaigns worked on the Obama Campaign of 2012 and on Senate races in 2014 in Colorado, Kansas, and Iowa.
- Bernie Sanders 2016 Presidential Run: this as been deemed by some a grassroots campaign because of its focus on small donations, massive rallies, and other grassroots style politicking methods.
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- Students for a Democratic Society. "Port Huron Statement". Retrieved 28 November 2015.
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- Courtesy: Eigen's Political & Historical Quotations "Beveridge, Albert J.". 2006-05-20.
- "New-York tribune. (New York [N.Y.]) 1866-1924, September 09, 1907, Page 4, Image 4". loc.gov.
- "The Salt Lake herald. (Salt Lake City [Utah]) 1870-1909, September 25, 1903, Last Edition, Page 6, Image 6". loc.gov.
- Baletti, Brenda; Wolford, W; Johnson, Tamara. "Late Mobilization: Transnational Peasant Networks and Grassroots Organizing in Brazil and South Africa". Journal of Agrarian Change 8 (2-3): 290. doi:10.1111/j.1471-0366.2008.00171.x. Retrieved 26 October 2015.
- Wang, Xu (1997). "Mutual Empowerment of State and Peasantry: Grassroots Democracy in Rural China". World Development 25 (9): 1431.
- Cnaan, Ram; Milofsky, Carl (2007). Handbook of Community Movements and Local Organization. New York: Springer. p. 362. ISBN 978-0-387-75729-2.
- Taylor, Dorceta; Bullard, Robert (1993). Confronting Environmental Racism: Voices from the Grassroots. Cambridge, MA: South End Press. p. 53. ISBN 0-89608-446-9.
- Barkan, Joanne (2012). "Hired Guns on Astroturf: How to Buy and Sell School Reform.". Dissent 59 (2): 49. Retrieved 16 November 2015.
- Walter Truett Anderson (January 5, 1996). "Astroturf – The Big Business of Fake Grassroots Politics".
- Cho, Charles (3 July 2011). "Astroturfing Global Warming: It Isn’t Always Greener on the Other Side of the Fence". Journal of Business Ethics 104 (4). Retrieved 18 November 2015.
- Wear, Rae (2014). "Astroturf and populism in Australia: The Convoy of No Confidence". Australian Journal of Political Science 49 (1). doi:10.1080/10361146.2013.864598. Retrieved 28 November 2015.
- Formisano, Ronald (Feb 14, 2012). The Tea Party. Baltimore: JHU Press. ISBN 978-1-4214-0610-7. Retrieved 28 November 2015.
- "Opinion: For grassroots sport to grow, funding model must be overhauled - Sports Business Insider". sportsbusinessinsider.com.au.
- "FIFA Courses - FIFA.com". FIFA.com.
- Staff writers (April 3, 2014). "FFA Play Football". Football Federation Australia.
- Gambino, Lauren; Jacobs, Ben. ""Grassroots movement working": Bernie Sanders gains on the Clinton Machine". The Guardian. Retrieved 16 November 2015.
- Ekins, Paul (1992.) A new world order: grassroots movements for global change. Routledge. ISBN 0-415-07115-1
- Fox, Jonathan A.; Brown David, L. (1998.) The struggle for accountability: the World Bank, NGOs, and grassroots movements. Massachusetts Institute of Technology. ISBN 0-262-56117-4
- The Citizen's Handbook – guides to grassroots/community organizing