Foster care is a system in which a minor has been placed into a ward, group home (residential child care community or treatment centre), or private home of a state-certified caregiver, referred to as a "foster parent", or with a family member approved by the state. The placement of a "foster child" is normally arranged through the government or a social service agency. The institution, group home, or foster parent is compensated for expenses unless with a family member. Any adult who has spent time in care can be described as a "care leaver", especially in European countries.

The state, via the family court and child protective services agency, stand in loco parentis to the minor, making all legal decisions while the foster parent is responsible for the day-to-day care of the minor.

Scholars and activists have expressed concerns about the efficacy of foster care services provided by non-government organisations. Specifically, this pertains to poor retention rates of social workers. Poor retention rates are attributed to being overworked in an emotionally draining field that offers minimal monetary compensation. The lack of professionals pursuing a degree in social work coupled with poor retention rates in the field has led to a shortage of social workers and created large caseloads for those who choose to work and stay in the field. The efficacy of caseworker retention also affects the overall ability to care for clients. Low staffing leads to data limitations that infringe on caseworkers' ability to adequately serve clients and their families.

Foster care is correlated with a range of negative outcomes compared to the general population. Children in foster care have a high rate of ill health, particularly psychiatric conditions such as anxiety, depression, and eating disorders. One third of foster children in a US study reported abuse from a foster parent or other adult in the foster home. Nearly half of foster children in the US become homeless when they reach the age of 18, and the poverty rate is three times higher among foster care alumni than in the general population.

In Australia foster care was known as "boarding-out". Foster care had its early stages in South Australia in 1867 and stretched to the second half of the 19th century. It is said that the system was mostly run by women until the early 20th century. Then the control was centered in many state children's departments. "Although boarding-out was also implemented by non-government[al] child rescue organizations, many large institutions remained. These institutions assumed an increasing importance from the late 1920s when the system went into decline." The system was re-energized in the postwar era, and in the 1970s. The system is still the main structure for "out-of-home care". The system took care of both local and foreign children. "The first adoption legislation was passed in Western Australia in 1896, but the remaining states did not act until the 1920s, introducing the beginnings of the closed adoption that reached it peak in the period 1940–1975. New baby adoption dropped dramatically from the mid-1970s, with the greater tolerance of and support for single mothers".

Foster care in Cambodia is relatively new as an official practice within the government. However, despite a later start, the practice is currently making great strides within the country. Left with a large number of official and unofficial orphanages from the 1990s, the Cambodian government conducted several research projects in 2006 and 2008, pointing to the overuse of orphanages as a solution for caring for vulnerable children within the country. Most notably, the studies found that the percentage of children within orphanages that had parents approached 80%. At the same time, local NGOs like "Children In Families" began offering limited foster care services within the country. In the subsequent years, the Cambodian government began implementing policies that required the closure of some orphanages and the implementation of minimum standards for residential care institutions. These actions lead to an increase in the number of NGOs providing foster care placements and helped to set the course for care reform around the country. As of 2015, the Cambodian government is working with UNICEF, USAID, several governments, and many local NGOs in continuing to build the capacity for child protection and foster care within the Kingdom.

Foster children in Canada are known as permanent wards (crown wards in Ontario). A ward is someone, in this case a child, placed under protection of a legal guardian and are the legal responsibility of the government. Census data from 2011 counted children in foster care for the first time, counting 47,885 children in care. The majority of foster children – 29,590, or about 62 per cent – were aged 14 and under. The wards remain under the care of the government until they "age out of care". All ties are severed from the government and there is no longer any legal responsibility toward the youth. This age is different depending on the province.

In December 2013, the Israeli Knesset approved a bill co-drafted by the Israel National Council for the Child to regulate the rights and obligations of participants in the foster care system in Israel.