In the past decade, interest and activities in the interface between primary health care and mental health and substance abuse services have increased markedly among the many stakeholders who care about positive outcomes for young children’s mental health and well-being. Building on that increased interest, this document was developed as a resource to give health care providers and policy makers at all levels an overview of a range of innovative efforts across the country where health care providers have attempted to treat families as a whole, provide care in the context of a medical home, identify mental health and substance abuse disorders earlier, and make successful referrals and linkages to community-based mental health and substance abuse services and supports. Primary health care providers represent a significant and natural point of contact for young children and their families. Being able to intervene early with caregivers of infants and toddlers through primary health care can promote children’s mental health and wellbeing, prevent or delay later negative outcomes, promote protective factors and decrease risk factors associated with negative child outcomes, and may prevent the need for intensive and expensive care at a later age. This document includes a relevant literature section, eight case studies of primary care sites using innovative approaches to serve pregnant women and/or families with children birth to three years old, a synthesis of these approaches, lessons learned, and strategies to assist others in replicating these approaches.