his article illustrates the problems faced and the techniques used by the linguist when acting as an expert witness. Examples are drawn from a wide variety of cases.The article first exemplifies disputes about the meaning of individual morphemes in a trademark case, where the American burger chain McDonalds claimed ownership of the morpheme ‘Mc’ on the grounds that they had invented a ‘McLanguage’, and aboutthe interpretation of individual word like ‘sufficient’, ‘preclude’ and ‘impairment’ in jury instructions and health insurance proposals, where convincing evidence is offered that cooperative readers would not have derived the meaning intended by the legal authors of the texts. The article then examines the contribution linguists made in two specific cases to resolving questions about the degree of grammatical complexity in a disputed letter and a statute whose interpretation had been appealed, before moving on to use the concept of linguistic uniqueness to help resolve the question of the ‘ownership’ of particular words and phrases in two cases of suspected plagiarism. The concepts used in the plagiarism cases are then used to resolve a dispute about whether a whole interview record had been fabricated by the police in a murder case. Throughout the article examples are provided of the wide range of techniques that forensic linguists have developed and now use to reach and support their opinions, ranging from evidence derived from corpora and questionnaires to insights drawn from morphology, grammar, lexis, pragmatics, semantics and discourse and text analysis.