In legal practice, a change of circumstances is a supervening event that materially alters the facts on which a right, obligation, order or valuation was based.It is a descriptive expression, not a defined term. In contract law across the UK and Ireland, such changes may engage a force majeure clause or, exceptionally, the doctrine of frustration (where performance becomes impossible or radically different).In family law, parties commonly invoke a material change of circumstances to seek variation, suspension or discharge of periodical payments (spousal maintenance) and child maintenance/support, or to vary child arrangements/contact orders. Variation is governed by statute and case law: for example the Matrimonial Causes Act 1973, the Child Support Act 1991 (Great Britain) and the Child Support (Northern Ireland) Order 1991, and in Ireland the Family Law (Maintenance of Spouses and Children) Act 1976 and Family Law (Divorce) Act 1996. Decision‑makers assess materiality, durability and fairness; a child’s welfare is paramount.In rating/valuation, a material change of circumstances (MCC) can justify altering a non‑domestic rating list on appeal, typically for physical changes to the hereditament or its locality, under the Local Government Finance Act 1988, with analogous regimes in Scotland, Northern Ireland and Ireland.