Child custody describes, in everyday legal practice, who is responsible for a child’s day‑to‑day care, where the child lives and who makes major decisions about the child’s upbringing after parental separation or state intervention. In the UK and Ireland it is now largely a non-technical or historical term: modern statutes and courts typically refer instead to “parental responsibility” and “child arrangements” (England and Wales), “residence” and “contact” (Northern Ireland), “parental responsibilities and rights” and “residence orders” (Scotland), and “guardianship”, “custody” and “access” (Ireland). Although “custody” still appears in some Irish legislation and older UK case law, most current proceedings concern orders regulating residence, contact and decision‑making rather than “custody” as such. The concept is central in private law disputes between parents and in public law care proceedings, where courts may allocate parental responsibility, determine living arrangements, or authorise local authority/HSE intervention. Across all four jurisdictions, the child’s welfare or best interests are the paramount or first and overriding consideration when determining custody-type issues, alongside factors such as safety, continuity of care and the child’s views, depending on age and maturity.