This chapter will focus on the theory behind and research on Parent-Child Interaction Therapy (PCIT), a treatment developed for young children with disruptive behavior problems. We will describe and provide details about PCIT, which is based on both attachment and social learning models, and incorporates an innovative approach to treatment in which therapists coach caregivers "live" via a wireless headset while each caregiver interacts with their child. In addition, we will review research that has examined PCIT with a variety of diverse populations (e.g., children with developmental delay, physical abuse histories, anxiety and depression, and children from underrepresented racial and ethnic minority families), settings (e.g., clinic, home, school) and formats (e.g., individual, group, intensive). Finally, we will present a case study of PCIT with a child younger than 2 years to demonstrate the effectiveness of PCIT and highlight some common challenges and pitfalls that clinicians may face in clinical practice.