In biological terms, a community is a group of interacting organisms sharing an environment. In human communities, intent, belief, resources, preferences, needs, risks, and a number of other conditions may be present and common, affecting the identity of the participants and their degree of cohesiveness. In sociology, the concept of community has caused infinite debate, and sociologists are yet to reach agreement on a definition of the term. In deed, one can find 94 discrete definitions of the term even as early as mid-1950s. Traditionally a "community" has been defined as a group of interacting people living in a common location. The word is often used to mean a group that is organised around common values and social cohesion within a shared geographical location, generally in social units larger than a household. However, the definition has evolved and been enlarged to mean individuals who share characteristics, regardless of their location or type of interaction. In this sense, "community" can mean a community of interest or an ethnic group. Finally, wider meanings of the word can refer to the national community or global community. What these various meanings have in common is that they refer to the strength of the ties between the group, of whatever nature—cultural, ethnic, or moral—they may be. Communis comes from a combination of the Latin prefix com- (which means "together") and the word munis (which has to do with the exchange of services), probably originally derived from the Etruscan word munis- (meaning "to endow", or "to have the charge of").
During their growth and maturation, people encounter a variety of individuals and experiences. Infants first interact with their immediate family, then with extended family. As they mature, children interact with the local community, first in school and later through work. They thus develop individual and group identity through associations that connect them to life-long community experiences.
As people grow, they learn about and form perceptions of social structures. During this progression, they form personal and cultural values, a world view, and attitudes toward the larger society. Gaining an understanding of group dynamics and how to "fit in" is part of socialization. Individuals develop interpersonal relationships and begin to make choices about whom to associate with and under what circumstances.
During adolescence and adulthood, the individual tends to develop a more sophisticated identity, often taking on a role as a leader or follower in groups. If an individual develops the feeling that they belong to a group, and they must help the group they are part of, then they develop a sense of community.
If community exists, both freedom and security exist as well. The community then takes on a life of its own, as people become free enough to share and secure enough to get along. The sense of connectedness and formation of social networks comprise what has become known as social capital.
Social capital is defined by Robert D. Putnam as "the collective value of all social networks (who people know) and the inclinations that arise from these networks to do things for each other (norms of reciprocity). Social capital in action can be seen in groups of varying formality, including neighbours keeping an eye on each others' homes. However, as Putnam notes in Bowling Alone: The Collapse and Revival of American Community (2000), social capital has been falling in the United States. Putnam found that over the past 25 years, attendance at club meetings has fallen 58 percent, family dinners are down 33 percent, and having friends visit has fallen 45 percent.
The same patterns are also evident in several other western countries. Western cultures are thus said to be losing the spirit of community that once were found in institutions including churches and community centers. Sociologist Ray Oldenburg states in The Great Good Place that people need three places: 1) the home, 2) the office, and, 3) the community hangout or gathering place. With this philosophy in mind, many grassroots efforts such as The Project for Public Spaces are being started to create this "Third Place" in communities. They are taking form in independent bookstores, coffeehouses, local pubs, and through many innovative means to create the social capital needed to foster the sense and spirit of community.
In a seminal 1986 study, McMillan and Chavis identify four elements of "sense of community": 1) membership, 2) influence, 3) integration and fulfillment of needs, and 4) shared emotional connection. They give the following example of the interplay between these factors:
Someone puts an announcement on the dormitory bulletin board about the formation of an intramural dormitory basketball team. People attend the organizational meeting as strangers out of their individual needs (integration and fulfillment of needs). The team is bound by place of residence (membership boundaries are set) and spends time together in practice (the contact hypothesis). They play a game and win (successful shared valent event). While playing, members exert energy on behalf of the team (personal investment in the group). As the team continues to win, team members become recognized and congratulated (gaining honor and status for being members). Someone suggests that they all buy matching shirts and shoes (common symbols) and they do so (influence).
A Sense of Community Index (SCI) has been developed by Chavis and colleagues and revised and adapted by others. Although originally designed to assess sense of community in neighborhoods, the index has been adapted for use in schools, the workplace, and a variety of types of communities.
In ecology, a community is an assemblage of populations of different species, interacting with one another. Community ecology is the branch of ecology that studies interactions between and among species. It considers how such interactions, along with interactions between species and the abiotic environment, affect community structure and species richness, diversity and patterns of abundance. Species interact in three ways: competition, predation and mutualism. Competition typically results in a double negative—that is both species lose in the interaction. Predation is a win/lose situation with one species winning. Mutualism, on the other hand, involves both species cooperating in some way, with both winning.
The process of learning to adopt the behavior patterns of the community is called socialization. The most fertile time of socialization is usually the early stages of life, during which individuals develop the skills and knowledge and learn the roles necessary to function within their culture and social environment. For some psychologists, especially those in the psychodynamic tradition, the most important period of socialization is between the ages of one and ten. But socialization also includes adults moving into a significantly different environment, where they must learn a new set of behaviors.
Socialization is influenced primarily by the family, through which children first learn community norms. Other important influences include school, peer groups, mass media, the workplace, and government. The degree to which the norms of a particular society or community are adopted determines one's willingness to engage with others. The norms of tolerance, reciprocity, and trust are important "habits of the heart," as de Tocqueville put it, in an individual's involvement in community.
Community development, often linked with Community Work or Community Planning, is often formally conducted by non-government organisations (NGOs), universities or government agencies to improve the social well-being of local, regional and, sometimes, national communities. Less formal efforts, called community building or community organizing, seek to empower individuals and groups of people by providing them with the skills they need to effect change in their own communities. These skills often assist in building political power through the formation of large social groups working for a common agenda. Community development practitioners must understand both how to work with individuals and how to affect communities' positions within the context of larger social institutions.
Formal programs conducted by universities are often used to build a knowledge base to drive curricula in sociology and community studies. The General Social Survey from the National Opinion Research Center at the University of Chicago and the Saguaro Seminar at the John F. Kennedy School of Government at Harvard University are examples of national community development in the United States. In The United Kingdom, Oxford University has led in providing extensive research in the field through its Community Development Journal, used worldwide by sociologists and community development practitioners.
At the intersection between community development and community building are a number of programs and organizations with community development tools. One example of this is the program of the Asset Based Community Development Institute of Northwestern University. The institute makes available downloadable tools to assess community assets and make connections between non-profit groups and other organizations that can help in community building. The Institute focuses on helping communities develop by "mobilizing neighborhood assets" — building from the inside out rather than the outside in.
More recently Peck remarked that building a sense of community is easy but maintaining this sense of community is difficult in the modern world. Community building can use a wide variety of practices, ranging from simple events such as potlucks and small book clubs to larger–scale efforts such as mass festivals and construction projects that involve local participants rather than outside contractors.
Community building that is geared toward citizen action is usually termed "community organizing." In these cases, organized community groups seek accountability from elected officials and increased direct representation within decision-making bodies. Where good-faith negotiations fail, these constituency-led organizations seek to pressure the decision-makers through a variety of means, including picketing, boycotting, sit-ins, petitioning, and electoral politics. The ARISE Detroit! coalition and the Toronto Public Space Committee are examples of activist networks committed to shielding local communities from government and corporate domination and inordinate influence.
Community organizing is sometimes focused on more than just resolving specific issues. Organizing often means building a widely accessible power structure, often with the end goal of distributing power equally throughout the community. Community organizers generally seek to build groups that are open and democratic in governance. Such groups facilitate and encourage consensus decision-making with a focus on the general health of the community rather than a specific interest group. The three basic types of community organizing are grassroots organizing, coalition building, and "institution-based community organizing," (also called "broad-based community organizing," an example of which is faith-based community organizing, or "congregation-based community organizing").
Community service is usually performed in connection with a nonprofit organization, but it may also be undertaken under the auspices of government, one or more businesses, or by individuals. It is typically unpaid and voluntary. However, it can be part of alternative sentencing approaches in a justice system and it can be required by educational institutions.
A number of ways to categorize types of community have been proposed; one such breakdown is:
Communities are nested; one community can contain another—for example a geographic community may contain a number of ethnic communities.
In some contexts, "community" indicates a group of people with a common identity other than location. Members often interact regularly. Common examples in everyday usage include:
Some communities share both location and other attributes. Members choose to live near each other because of one or more common interests.
Definitions of community as "organisms inhabiting a common environment and interacting with one another, while scientifically accurate, do not convey the richness, diversity and complexity of human communities. Their classification, likewise is almost never precise. Untidy as it may be, community is vital for humans. Scott Peck expresses this in the following way: "There can be no vulnerability without risk; there can be no community without vulnerability; there can be no peace, and ultimately no life, without community.