Section 1503 of Title 18 of the United States Code forbids two kinds of conduct: influencing, intimidating, or impeding any witness, juror, or court official and, more generally, influencing, obstructing, or impeding the due administration of justice. Elements of a Section 1503 offense are discussed in detail, along with relevant case law and defenses. Section 1512, the main provision of the Victim and Witness Protection Act of 1982 (VWPA), is also described, along with elements of the offense of tampering with a witness. Apparent conflicts between Sections 1503 and 1512 are identified and discussed, with the observation that most Federal circuit courts have held that the enactment of the VWPA does not preclude the prosecution of non-coercive witness tampering under Section 1503 of Title 18. However, the affirmative defense provision of Section 1512 of VWPA appears to be vulnerable to constitutional challenge. 138 footnotes.