Newly discovered evidence refers to material that existed at the time of the original trial or hearing, but which was not known to, and could not reasonably have been discovered by, the party seeking to rely on it. It commonly arises in appeals, applications to set aside judgments, and applications for criminal case review.Across England & Wales, Scotland, Northern Ireland and Ireland, courts generally require that such evidence: (i) is genuinely new; (ii) could not with reasonable diligence have been obtained earlier; (iii) is credible and admissible; and (iv) could have had an important, often decisive, impact on the outcome. These principles are derived mainly from case law, and their precise formulation varies by jurisdiction and context (civil or criminal).In criminal proceedings, newly discovered evidence often underpins arguments that a conviction is unsafe or a miscarriage of justice has occurred, including references to Criminal Cases Review Commissions or equivalent bodies. In civil litigation, it may justify an appeal out of time, or an application to reopen proceedings or set aside default or summary judgment, particularly where fraud, mistake or procedural irregularity is alleged.