Modern social work employs three methods of assistance: case work, group work, and community organization. Case work is the method by which individual persons and families are assisted. The person in need of case work may be physically, mentally, or socially handicapped. Among those regarded as socially handicapped are: the unemployed, the homeless, members of broken families, alcoholics, drug addicts, and neglected or problem children. To determine the cause of maladjustment, the social worker must understand individual psychology as well as the sociology of the community. Physicians, psychiatrists, and other specialists may be required to help diagnose the difficulty.

Social group work is exemplified by the social settlement, the supervised playground and gymnasium, and the classroom, where handicrafts may be learned. The community may be called upon to provide the buildings and grounds for such activities; often the services of volunteers and of public groups are utilized; in recent years people living in poverty areas have been employed to work in and direct poverty projects in their own communities.

Through community organization the welfare work of single agencies as well as of whole communities is directed, cooperation between public and private agencies is secured, and funds are raised and administered. The funds required by private agencies are often pooled in a community chest, from which each agency receives a share. Community welfare councils are organized to map programs of rehabilitation, to eliminate duplication of services, and to discover and meet overlooked needs.

Social work emerged as a profession out of the early efforts of churches and philanthropic groups to relieve the effects of poverty, to bring the comforts of religion to the poor, to promote temperance and encourage thrift, to care for children, the sick, and the aged, and to correct the delinquent. Orphanages and homes for the elderly were typical results of these activities. The word charity best describes the early activities, which were aimed at the piecemeal alleviation of particular maladjustments. In such charitable work the principal criterion in determining aid to families was worthiness, while the emphasis in later social work was on restoring individuals to normal life both for their own sake and for the sake of the community.

The first attempts to solve the problem of poverty in a modern scientific way was made by P. G. F. Le Play, who in the 1850s made a detailed study of the budgets of hundreds of French workers' families. Forty years later Charles Booth investigated wages and prices, working conditions, housing and health, standards of living, and leisure activities among the poor of London and revealed the extreme poverty of a third of the population. Booth's social survey became a method for determining the extent of social maladjustment, and through surveys in other cities in Europe and the United States a vast number of facts were accumulated, and methods were developed that provided the basis for modern social work.

In 1874 the National Conference of Charities and Correction (now called the National Conference on Social Welfare) was organized in the United States. Public relief and private philanthropic effort remained largely matters of local and state concern until after 1930, when the federal government entered the field of social work on a large scale to cope with the effects of the Great Depression. Resources were made available, the number of social workers was greatly increased, and it became necessary to coordinate public and private activities. Social work has been steadily professionalized, and special graduate schools as well as departments in universities have been established to train social workers. By 1999 there were 377 accredited undergraduate schools of social work in the United States.