Despite the liberalization of competency requirements for child witnesses in many countries (Spencer & Flin, 1993; Youth Justice and Criminal Evidence Act, 1999, s. 53 [Engl.]), a substantial number of courts in the United States and other countries require that every witness take the oath or make some sort of affirmation that s/he will tell the truth (Federal Rules of Evidence 602,2001;Shrimpton, Oates, & Hayes, 1996).In order to guarantee that an oath or affirmation is understood by child witnesses, courts routinely inquire into children's understanding of the difference between the truth and lies and their obligation to tell the truth (Myers, 1997). Even when unsworn testimony is allowed, many jurisdictions require child witnesses to demonstrate an appreciation of their duty to tell the truth (Flin, Kearney, Murray, 1996; Fla. Stat. Ch. 90.605, 1999 (US); Ho, 1996; Pipe & Henaghan, 1996). Moreover, many courts continue to conduct oath-taking competency hearings in spite of legislatively enacted presumptions of competency (Gold, 1992;Cashmore, 1995).Regardless of a jurisdiction's competency requirements, investigators and attorneys routinely ask child witnesses about the truth and lies under the theory that children's understanding is evidence of veracity (Spencer & Flin, 1993).