RULES OF EVIDENCE
The federal courts are guided by the Federal Rules of Evidence (FRE) and the Federal Rules of Civil Procedure (FRCP), which are generally applied to state cases as well.

FRE 401 and 402 relate to the relevancy, and thus admissibility, of evidence and FRCP Rule 26(b)(1) identifies the relevant information that can be obtained barring privilege. FRE 501 and 502 deal with protections for relevant information, while 502 also relieves some of the burden of privilege review.

FRE Rule 702 {Daubert trilogy "Testimony by Experts"} is being revised in 2022 to: A witness who is qualified as an expert by knowledge, skill, experience, training, or education may testify in the form of an opinion or otherwise if the proponent has demonstrated by a preponderance of the evidence that: (1) the expert’s scientific, technical, or other specialized knowledge will help the trier of fact to understand the evidence or to determine a fact in issue (2) the testimony is based on sufficient facts or data (3) the testimony is the product of reliable principles and methods (4) the expert’s opinion reflects a reliable application of the principles and methods to the facts of the case.

FRE Rule 802 addresses the handling of hearsay, and both Rule 803(6) and 803(7) allow hearsay if the source is deemed reliable, such as an expert in the relevant field which is addressed by Rule 702.

FRE Rule 901 addresses the authentication of such evidence through forensic testing or by virtue of its source.

FRE Rule 902(14) {codified December 1st, 2017}. Electronically copied data, if authenticated by a process of digital identification as shown by a certification of a qualified person, shall be deemed as Self-Authenticating evidence and admitted without extrinsic evidence of authenticity. Otherwise, a certification in the form of a written affidavit by a qualified person, capable of being a witness at trial, shall be required to establish authenticity. 

FRE 1002 relates to best evidence, and requires the production of the original or a satisfactory explanation for its exception.

FRE Rule 1003. A duplicate is admissible to the same extent as the original unless a genuine question is raised about the original’s authenticity or the circumstances make it unfair to admit the duplicate.

FRE Rule 1006. A summary may serve as substitute evidence so long as the underlying evidence is made available.

FRCP Rule 26. Duty to Disclose governs what needs to be disclosed to the parties and court, and when this must occur.

FRCP Rule 37(e) Failure to Preserve Electronically Stored Information. If electronically stored information that should have been preserved in the anticipation or conduct of litigation is lost because a party failed to take reasonable steps to preserve it, and it cannot be restored or replaced through additional discovery, the court:
 (1) upon finding prejudice to another party from loss of the information, may order measures no greater than necessary to cure the prejudice; or
 (2) only upon finding that the party acted with the intent to deprive another party of the information’s use in the litigation may:
  (A) presume that the lost information was unfavorable to the party;
  (B) instruct the jury that it may or must presume the information was unfavorable to the party; or
  (C) dismiss the action or enter a default judgment.

The Frye standard is a general acceptance test to determine the admissibility of scientific evidence. Expert opinion based upon a scientific technique is admissible only where the technique is generally accepted as reliable in the relevant scientific community.