Young children (birth to age 5) are more likely to be expelled or suspended than school-aged children, but we know comparatively little about the precursors to and prevention of exclusion in early childhood settings. Furthermore, what research has been conducted has not been systematically synthesized to inform policy and funding decisions. The present review seeks to determine how early childhood exclusion is defined and assessed in the academic literature. Studies measuring early childhood suspension or expulsion were systematically gathered and coded for study characteristics, definitions, and measures of exclusionary discipline and disparity, and factors associated with exclusion rates. Results (n = 20) show an accelerating pace of inquiry that attends to multiple levels of the ecological system (children, teachers, and programs) across diverse settings (home-, center-, and school-based care). Additional research that draws on data spanning multiple types of early care and education settings is needed to inform legislation and intervention funding decisions. (author abstract)