The "DC:0-5[TM]: Diagnostic Classification of Mental Health and Developmental Disorders of Infancy and Early Childhood" (DC:0-5) includes significant revisions, making it a substantially different diagnostic framework from its predecessor, DC:0-3R. The Nordic countries have a long history of using the DC system. The Nordic DC:0-5 collaboration was formalized in 2015 when a Nordic DC:0-5 working group was initiated by the Nordic affiliation of the World Association of Infant Mental Health (NAIMH) and the Finnish affiliation PIRPANA. This article describes efforts to explore applicability of the DC:0-5 during introduction training courses and supervision sessions. The revised DC:0-5 is overall considered an improvement over earlier experiences with DC:0-3R. In this article, the authors present reflections and experiences from clinicians, researchers, students, and trainers who have provided feedback about training and use of the DC:0-5 system from the first 5 years of implementation.