Relevant evidence describes material that, if accepted, could rationally affect the assessment of a fact in issue or of a fact relevant to it. In England & Wales and Northern Ireland, the common-law test, stated in DPP v Kilbourne [1973] AC 729, is whether the evidence is logically probative or disprobative. Irish courts apply the same test at common law. Scots law likewise treats evidence as relevant if it bears upon the facts in issue; the familiar formulation is “competent, relevant and admissible”.Relevance is a threshold for admissibility but not sufficient on its own. Courts may exclude relevant evidence under specific exclusionary rules (e.g., hearsay, opinion, collateral/character, privilege) or discretionary/fairness controls-PACE 1984 s78 (E&W), PACE (NI) Order 1989 art 76 (NI), Lawrie v Muir 1950 JC 19 (Scotland), and constitutional fairness in Ireland (e.g., DPP v JC [2015] IESC 31). If admitted, relevance influences weight and probative value; judges manage exclusion where probative value is outweighed by unfair prejudice or disproportionate cost or delay.Usage is broadly consistent across the four jurisdictions; differences concern particular exclusionary regimes and, in Scottish criminal cases, the separate requirement of corroboration (sufficiency, not relevance).