Community organizing generally involves those local residents coming together into an inclusive, accessible organization to pursue shared goals.
Problems and Purpose
Community organizing, broadly speaking, is the process whereby people living in proximity to each other come together into an organization that acts in their shared self-interest. Generally, organizers assume that social change will necessarily involve some element of conflict and struggle, as opposed to consensus, in order to generate collective power for the powerless. The process aims to generate durable power for the community organization, such that it can influence key decision-makers on a range of important issues over time. Community organizers work with and develop new local leaders, facilitating coalitions and developing campaigns. 
Community organizers typically aim to create democratically-governed groups, which are inclusive and accessible to the members of the community, and focus on specific interest groups rather than the community as a whole. Organizing seeks to broadly empower community members, with the end goal of "distributing" power more equally throughout the community. 
Community organizing is not to be confused with community development, which focuses more on consensus and is usually directed by educated professionals working in government, non-profit, or business organizations. Community development projects increasingly involve community participation and seek to empower residents in impoverished areas with skills and training, but the process generally assumes that collaboration to solve community challenges can occur between groups and individuals without conflict or power struggles. One popular form is asset-based community development, which focuses on seeking out existing strengths in the community. Yet, the relationship between community organizing and community development is nuanced, as the literature is similar, and since the 1970s, community development practitioners have been influenced by structural analyses of inequity and power distribution. 
Origins and Development
Community Organizing in the United States
Robert Fisher and Peter Romanofsky identify four rough periods for community organizing in the US: 
1. 1880 to 1900
People organized immigrant neighbourhoods in urban centres to meet the pressures of rapid immigration and industrialization. The dominant approach is termed social work by Fisher since the organizers focused on building community through settlement houses and other service mechanisms.
2. 1900 to 1940
Community organizing methodology was generated in Schools of Social Work during this period, grounded in the philosophy of John Dewey, which focused on experience, education, and other sociological concepts. Anti-capitalist doctrines were relevant during this period and organizations tended to be nationally focused during the depression era since change regarding economic issues seemed more likely at the national rather than neighbourhood level.
3. 1940 to 1960
Chicago-based Saul Alinksy is credited with originating the term community organizer. Alinksy was the founder of the first national community organizing training network, as well as the first to codify key strategies and aims of community organizing in his books, Reveille for Radicals, published in 1946, and and Rules for Radicals, published in 1971.
The following excerpts from Reveille for Radicals give a good sense of Alinsky's perspective on organizing and of his public style of engagement :
A People's Organization is a conflict group, [and] this must be openly and fully recognized. Its sole reason in coming into being is to wage war against all evils which cause suffering and unhappiness. A People's Organization is the banding together of large numbers of men and women to fight for those rights which insure a decent way of life....
A People's Organization is dedicated to an eternal war. It is a war against poverty, misery, delinquency, disease, injustice, hopelessness, despair, and unhappiness. They are basically the same issues for which nations have gone to war in almost every generation.... War is not an intellectual debate, and in the war against social evils there are no rules of fair play....
A People's Organization lives in a world of hard reality. It lives in the midst of smashing forces, dashing struggles, sweeping cross-currents, ripping passions, conflict, confusion, seeming chaos, the hot and the cold, the squalor and the drama, which people prosaically refer to as life and students describe as "society."
4. 1960 to present
The civil rights movement, anti-war movements, Chicano movement, feminist movement, and gay rights movement all influenced and were influenced by ideas of neighbourhood organizing. "Experience with federal anti-poverty programs and the upheavals in the cities produced a thoughtful response among activists and theorists in the early 1970s that has informed activities, organizations, strategies and movements through the end of the century. Less dramatically, civic associations and neighborhood block clubs were formed all across the country to foster community spirit and civic duty, as well as provide a social outlet." 
Loss of urban communities
During these recent decades, the process of white flight where middle-class Americans move out of predominantly Black regions, and the professionalization of community organizations into 501(c)(3) non-profits, contributed to the dissolution of tight ethnic and racial communities. Therefore, community organizers began moving away from efforts to mobilize existing communities and towards creating and fostering relationships between community members. While organizers like Alinksy had long worked with churches, these trends led to increased congregational organizing in the 1980s, as one of few broad-based community institutions remaining. 
Emergence of national organizing support organizations
Training and support organizations for national coalitions "of mostly locally governed and mostly FBCO community organizing groups were founded in the Alinsky tradition. The Industrial Areas Foundation was the first, created by Alinsky himself in 1940. The other key organizations include ACORN, PICO National Network, Direct Action and Research Training Center, and the Gamaliel Foundation."  The organizer's role was "professionalized" such that it could be more like a long-term career than a brief, unfunded interlude. Training by these "umbrella" organizations enabled a common language around organizing to emerge among local volunteer leaders while expanding their skills. The Midwest Academy, based in Chicago, provides week-long training in organizing nationally to organizers and leaders who are not part of these established national organizations. The Center for Third World Organizing provides training focused on "change efforts in communities of color." CTWO advocates a process in which those that are most impacted are leading the fight for social change. CTWO offers multiple trainings that provide the tools needed to become an effective organizer.
The distinction between an "organizer" who staffs a community organization and "leaders" who make decisions and provide the public face of their groups was increasingly standardized over these years, even in many organizations not linked to "umbrella" training groups as the Alinsky tradition became increasingly influential.
Participant Recruitment and Selection
Neighbourhood and community organizations are typically open to all and specifically address community members. However, informal hierarchies and exclusionary mechanism might be at work.
How it Works: Process, Interaction, and Decision-Making
Influence, Outcomes, and Effects
Analysis and Lessons Learned
 Community organizing. Wikipedia. Last edited 1/26/2021, https://en.wikipedia.org/wiki/Community_organizing
 Robert Fisher and Peter Romanofsky. (1961). Community Organizing for Urban Social Change: A Historical Perspective: Greenwood Press.
 Alinsky, Saul (1987/1946). Reveille for Radicals. New York: Vintage.
Lead image: "Tenants of 85 Bowery and housing advocates protest in front of the Department of Buildings office at 280 Broadway in Manhattan on April 26" Linda Rosier/amNewYork https://goo.gl/8cY1tB
Secondary image: Members of the 83-85 Bowery Tenants Association, Getty Images https://goo.gl/gdGWqh