In 2017, the Office of Planning, Research, and Evaluation in the Administration for Children and Families funded Mathematica to conduct the Infant and Toddler Teacher and Caregiver Competencies (ITTCC) project. The project aims to examine existing efforts across states, institutions of higher education, professional organizations, and early care and education programs related to competencies for infant and toddler teachers and caregivers who work in group settings and build a conceptual foundation to inform future measurement, research, and evaluation. The findings described in this brief are based on an exploration of online competency-based professional development (PD) systems that include infant and toddler teachers and caregivers as an audience. Definitions for key terms (competency, competency framework, competency-based professional development, proficiency levels) as used in this project can be found on page 13. This brief is accompanied by a series of profiles of the PD systems selected for the exploration. The profiles include citations for all of the information reviewed to develop both the profiles and this brief. This brief includes citations for specific examples referenced in this brief. (author abstract)