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 Texas, evidence is governed by the Texas Rules of Evidence, which align with the Federal Rules of Evidence in many respects. Evidence, whether in physical or digital form, must be relevant to the issues in a legal dispute to be admissible in court. Relevance is determined by whether the evidence makes a fact more or less probable than it would be without the evidence and whether that fact is of consequence in determining the action. Expert witness testimony, as a specific form of evidence, must meet certain reliability standards before it can be admitted. In Texas, the reliability of expert testimony is assessed under the Daubert standard, which requires that the testimony is based on sufficient facts or data, is the product of reliable principles and methods, and that the expert has applied the principles and methods reliably to the facts of the case. The judge acts as the 'gatekeeper' to determine the admissibility of expert testimony, ensuring that only relevant and reliable evidence is presented to the jury or considered by the judge in a bench trial.