Evidence is information that exists in physical or digital form—such as written agreements and e-mail communications—as well as testimony from witnesses who have personal knowledge of facts relevant to a dispute. Evidence generally must be relevant to be admitted in court and considered by the factfinder (judge or jury) in resolving a lawsuit. And some forms of evidence, such as expert witness testimony, must be shown to be sufficiently reliable (as determined by the judge) to be admitted in evidence.

In Pennsylvania, evidence is crucial for resolving disputes in court and must be relevant to the issues at hand to be admissible. Relevance is determined by whether the evidence makes a fact more or less probable than it would be without the evidence, and if that fact is of consequence in determining the action. Physical evidence, such as written agreements, and digital evidence, like email communications, are subject to the same relevance standards. Testimony from witnesses with personal knowledge of the facts is also considered evidence. Expert witness testimony, in particular, must meet a reliability standard before it can be admitted. This is assessed by the judge based on the expert's qualifications, methodology, and the pertinence of their testimony to the case. Pennsylvania follows the Pennsylvania Rules of Evidence, which are similar to the Federal Rules of Evidence, in determining the admissibility of evidence in court. These rules are designed to ensure that the evidence presented is both reliable and pertinent to the case at hand.