Prior to the 20th century, services now handled by social workers were undertaken mostly by concerned individuals, churches, or private charities. The few government programs that did exist provided aid only to the completely destitute, in the belief that poverty was the result of personal shortcomings of the poor. In the 20th century, assistance to the poor and other needy persons has been integrated into a large array of welfare programs operated by governments at the national and local levels (see Welfare State).

Social workers are often caseworkers. This means that a worker is assigned to deal with specific families or individuals over a definite period of time—much as probation officers do with released delinquents. The origin of modern caseworkers can be traced to the appointment in England in the 1880s of medical social service workers called almoners. These individuals verified the financial eligibility of poor patients, provided counseling services to families suffering from ill health or loss, and gave home care for patients released from hospitals. The use of almoners soon spread to the United States. The first schools of social work appeared between 1890 and 1910 in London, New York City, and Amsterdam.

The major areas of concern for social workers are family, child, youth, and group welfare; assistance to the elderly; care for the ill and disabled; and welfare for the mentally ill. Family programs try to strengthen family units through economic assistance and a variety of services such as marriage counseling, family planning, and home meal services. Child welfare includes assistance to unwed mothers in addition to child health-care programs and aid to children whose home lives have been disrupted.

Most youth programs provide adult-supervised leisure-time activities (see Youth Organizations). They also involve dealing with runaways and correcting delinquency problems. Group-welfare workers help immigrants become adjusted and help resettle refugees (see Refugees). Assistance to the elderly includes transportation, senior-citizen centers, delivery of meals, nurse visitation, and reduced-cost medical supplies. Services to the ill or disabled include providing medication, rehabilitation, adjustment to handicaps, and nutrition assistance. Psychiatric social workers deal with the mentally ill from the time of diagnosis through hospitalization and rehabilitation. Rehabilitative measures may include the use of halfway houses, foster care, sheltered workshops, and regular employment.