The objective of the present study is to develop an Internet-delivered Parent-Child Interaction Therapy (PCIT) protocol for preschoolers with Oppositional Defiant Disorder (ODD) or Conduct Disorder (CD) and to evaluate via randomized controlled trial (RCT) the feasibility and acceptability of enrolling, retaining, and treating children with I-PCIT relative to traditional PCIT. Phase I will involve development of an Internet-delivered PCIT (I-PCIT) protocol and treatment materials, including therapist treatment manual and online session handouts. Phase II will entail a case series: the PI will treat 5 consecutive preschool ODD/CD cases with I-PCIT, affording opportunity to further work out any difficulties with protocol or equipment. Phase III will entail testing the feasibility and acceptability of I-PCIT in a pilot RCT conducted with 40 children (ages 3-5) meeting for a Diagnostic and Statistical Manual (DSM-IV) principal diagnosis of ODD or CD and their parent(s) randomly assigned to I-PCIT or traditional PCIT. Parents will provide informed consent. All eligible families will receive evidence based treatment. Treatment will either be either in-clinic Parent-Child Interaction Therapy (PCIT) or Internet-delivered PCIT (I-PCIT). Formal evaluations will be conducted at baseline, post-treatment, and 6-month follow-up. Families can opt to participate in two optional psychophysiological components of the study (one involving behavioral tasks while parents are monitored via physiological equipment, and one involving play tasks while children are monitored via physiological equipment). All assessments will be conducted in the Department of Psychology at Florida International University (FIU), in the Center for Children and Families.