Therapeutic playgroups provide a unique service for children with developmental delays and disabilities and their families, delivering tailored play-based therapy while facilitating parent support and community connections. Despite the prevalence of playgroups within the disability sector there is a paucity of research defining the key principles of therapeutic playgroups and their perceived benefits. Taking the perspectives of early intervention professionals this study sought to provide a definition of therapeutic playgroups and identify the “active ingredients” of therapeutic playgroups for children with developmental delays and disabilities. Focus group methodology was used to gather perspectives of 40 professionals with experience facilitating playgroups for children with developmental delays and/or disabilities and their families. Findings highlighted the complex nature of therapeutic playgroups which require an interplay of five “active ingredients” to be perceived as beneficial: facilitator and participant characteristics; playgroup structural characteristics, information provision, administration and logistical considerations. Therapeutic playgroups have distinct practice principles that distinguish them from other playgroups and therapeutic models for children with delays and disabilities and their families. This paper provides a definition of therapeutic playgroups, outlining the core practice principles for therapeutic playgroups, an essential step in developing and evaluating the effectiveness of therapeutic playgroups.