A last will and testament is a formal document by which a person (the testator) sets out how their property and other affairs are to be dealt with on death. It usually appoints executors (or, in Scotland, executors-nominate), directs the distribution of the estate, can create trusts, makes specific gifts and legacies, and may name guardians for minor children.Across the UK and Ireland it is a descriptive term rather than a single codified definition, but its essential features are similar: it is a revocable, ambulatory declaration of testamentary intentions that takes effect only on death and must comply with formal validity requirements. These are principally statutory, including the Wills Act 1837 (England and Wales and, with modifications, Northern Ireland), the Succession (Scotland) Act 1964 and the Succession Act 1965 (Ireland), together with extensive case law on capacity, knowledge and approval, and undue influence.The expression “last will and testament” is commonly used interchangeably with “will”. In practice, it is central to estate planning, probate and succession disputes, and to advising on intestacy risks, cross-border estates and the construction, rectification or challenge of testamentary instruments.