In 2017, the Office of Planning Research, and Evaluation (OPRE) in the Administration for Children and Families (ACF) funded Mathematica Policy Research 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 (ECE) programs related to competencies for I/T teachers and caregivers who work in group (center-based and family child care) settings and build a conceptual foundation to inform future measurement, research, and evaluation. The goal of this review was to examine what is known about the links between I/T teacher or caregiver competencies and outcomes in several areas (child, family, teacher/caregiver, classroom, and/or program). Specifically, we aimed to answer the following research questions: - What competencies of I/T teachers and caregivers have been examined in the literature? - What does evidence say about associations between I/T teacher and caregiver competencies and child, family, teacher/caregiver, classroom, and/or program outcomes? - Where are the gaps in the knowledge base pertaining to connections between I/T teacher/caregiver competencies and outcomes? (author abstract)