A joint defendant is a person or entity sued together with one or more others in the same legal proceedings, usually because they are alleged to be jointly or jointly and severally liable for the same wrong or obligation. The term is descriptive rather than formally defined in legislation, but is widely used in civil and criminal practice across England and Wales, Scotland, Northern Ireland and Ireland with broadly consistent meaning.In civil litigation, joint defendants commonly arise in claims for breach of contract, professional negligence, personal injury, construction disputes and contribution or indemnity claims, where responsibility or causation is contested between multiple parties. The status of joint defendant affects issues such as case management, disclosure, apportionment of liability, contribution between wrongdoers, costs orders and enforcement of judgments.In criminal proceedings, joint defendants (or “co‑accused” in Scottish practice) are individuals charged on the same indictment or complaint, often where joint enterprise, common purpose or conspiracy is alleged. Their joinder has procedural implications for admissibility of evidence, severance applications and directions to the jury.Rules on adding, removing or substituting joint defendants are governed by court rules (for example, CPR, RSC, Rules of the Court of Session) and relevant case law in each jurisdiction.