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 Maryland, evidence must be both relevant and reliable to be admissible in court. Relevance means that the evidence must have a direct bearing on the case, helping to prove or disprove a material fact in dispute. Reliability pertains to the quality of the evidence, ensuring that it is trustworthy and credible. For instance, expert witness testimony must be provided by someone with the requisite knowledge, skill, experience, training, or education in a particular field relevant to the case. The expert's methods and principles used to reach their conclusions must also be generally accepted in their field. Maryland courts follow the Maryland Rules of Evidence, which are similar to the Federal Rules of Evidence, in determining the admissibility of both physical and digital evidence, as well as witness testimony. The judge serves as the gatekeeper in deciding whether evidence meets these standards and is therefore admissible for consideration by the factfinder, which can be either a judge or a jury.