Early childhood education (ECE) teachers often lack the experience and skills to provide children with supports necessary to foster academic and social skill development. Professional development can improve ECE teachers' skills, but ECE trainers often lack understanding of adult learning principles, known as andragogy. Knowles' conceptual framework of andragogy was used to explore the knowledge and use of andragogical principles of 8 ECE trainers selected via criterion-based purposive sampling. The research questions focused on ECE trainers' knowledge and use of andragogical principles. Three cases, each consisting of 2 or 3 live professional development trainings for early childhood educators, were used in this study. Data sources included (a) observations of ECE trainings, (b) semi-structured interviews with ECE trainers, and (c) content analysis of ECE training materials. Thematic analysis revealed that although participants were not formally trained in andragogy and were unfamiliar with the associated verbiage, most had a strong grasp of andragogy and used andragogical principles to drive the development and presentation of their training materials. The 3 main themes that emerged were (a) lack of training/background in andragogy, (b) training strategies employed, and (c) training design. Findings from this study provide an original contribution to the limited existing research on the professional development of early childhood educators and expand the existing body of research on andragogy. This study contributes to social change by revealing that trainers may benefit from formal andragogical training, which may then improve the education provided by ECE teachers to young children.