The dynamics of child sexual abuse include: (1) progression of abuse; (2) duration of abuse; (3) lack of force and physical injury; (4) timing of disclosure of abuse; (5) the role of the non-offending parent/other family members; and (6) retraction and inconsistent statement. The article also includes a list of behavioral indicators of sexually abused children. In Canada there are two rules of evidence which inhibit the introduction of evidence of dynamics of sexual abuse in child sexual assault prosecutions. First, a party calling a witness cannot call evidence to bolster the credibility of its own witness. Second, the expert's evidence cannot usurp the function of the judge or jury. Expert evidence on the dynamics of sexual abuse should be tendered to explain conduct that is consistent with sexual abuse and which left unexplained might otherwise lead to the child being disbelieved. Behavioral indicators of child sexual abuse should be offered as confirming evidence of the child's complaint. The admissibility in American courts of expert testimony on child sexual abuse has been dealt with by a number of States; the article contains a brief review of several States' experiences. References, notes