In this article, the authors describe a 3-year initiative in New York state, led by the New York Center for Child Development (NYCCD), through which more than 2,500 mental health clinicians were trained in the DC:0-5. Funding was provided through the creative use of the Preschool Development, Birth to Five federally funded Block Grant, and collaborations are described with a public and a university partner to advance the dissemination and application of the classification system. The authors describe the "community of practice" follow-up sessions for trainees, targeted content workshops in infant and early childhood mental health (IECMH), and offering continuing education for professional development. Data from participant evaluations demonstrate the high impact of the training. The authors provide lessons learned in service of the question that Selma Frailberg asked more than 40 years ago: What about the baby?