Introduction: Family-focused cognitive behavioural therapy (FFCBT) is emphasized as an approach to optimize treatment outcomes for early-onset obsessive-compulsive disorder (OCD). Parental engagement is critical to successful treatment. However, few studies have examined how to promote parental engagement during FFCBT. Additionally, from a parental perspective, there is a limited understanding of factors that influence parental engagement throughout treatment, including the role of nurses. Aims: To determine (i) how parents experience and understand their engagement in FFCBT provided for their child with early-onset OCD in community or outpatient mental health programs, and (ii) how parents describe the role of nurses related to parental engagement during the treatment process. Methods: This study used an interpretive description approach. Semi-structured interviews were completed with parents (n = 17) recruited from community or outpatient children’s mental health programs in the Hamilton Region of Southwestern Ontario. Treatment provider interviews (n = 9) augmented the data collected from parents’ perceptions of their engagement and the role of nurses during FFCBT. Interviews were analyzed using Braun and Clark’s (2006) thematic analysis process. Results: A conceptualized model was constructed to display and communicate the individual, interpersonal, and contextual influences identified by parents and treatment providers. These influences facilitated or inhibited parental engagement during treatment across distinct phases, levels, and stages of engagement. Six distinct nursing roles were identified that promoted parental engagement throughout treatment. / Dissertation / Doctor of Philosophy (PhD) / Without effective treatment, pediatric obsessive-compulsive disorder (OCD) can interfere with childhood development. Early-onset OCD is a unique subtype of the disorder involving pediatric patients with symptoms that present before the age of 10 years. Family-focused cognitive behavioural therapy (FFCBT) emphasizing parental involvement is commonly used to treat pediatric OCD. However, parental engagement during FFCBT, including nurses’ roles, is poorly understood. This study aimed to increase knowledge about parental engagement during FFCBT for children with early-onset OCD receiving treatment in community programs. Data analysis of parent and treatment provider interviews identified various factors and how nurses influenced parental engagement during FFCBT. A model was made to display how these factors helped or hindered parental engagement during treatment and how nurses promoted engagement across three distinct phases. This new knowledge informed recommendations to promote parental engagement for treatment providers, improve service development and delivery, and strengthen nursing education.