Evidence

Evidence is:

Any observable event which tends to prove or disprove a proposition, see reality.
Any testimony or exhibit which is allowed to be considered by the trier of fact in a judicial or administrative proceeding.

Evidence in the United States federal courts

Prior to the 1905 enactment of the Federal Rules of Evidence (FRE), the rules of evidence were governed primarily by decisional law.
FRE 102 includes the following elements in the "Purpose and Construction" of the Federal Rules of Evidence:
"These rules shall be construed to..."

secure fairness in administration
eliminate unjustifiable expense and delay
promote growth and development of the law of evidence to the end that the truth may be ascertained, and proceedings justly determined

The following is the table of contents of the FRE:
I. General Provisions
Rule 101: Scope
Rule 102: Purpose and Construction
Rule 103: Rulings on Evidence
Rule 104: Preliminary Questions
Rule 105: Limited Admissibility
Rule 106: Remainder of or Related Writings or Recorded Statements
II. Judicial Notice
Rule 201: Judicial Notice of Adjudicative Facts
III. Presumptions in Civil Actions and Proceedings
Rule 301: Presumptions in General Civil Actions and Proceedings
Rule 302: Applicability of State Law in Civil Actions and Proceedings
the rest to come later

See: Affidavit, Corroborating evidence, Rebuttal, chain of custody

See also: Law