The quality of the parent-infant interaction is essential for the infant's development and is most objectively measured by observation. The existing observational tools for assessing parent-infant interaction were identified and described, and their psychometric soundness was evaluated. Twenty electronic databases from inception through June 2013 were searched. Validity was evaluated in five domains (test content, response process, internal structure, relations to other variables, and consequences). Of the 23,961 citations identified, 24 tools were included. Most tools demonstrated a valid rating procedure, reproducibility, and discriminant validity, based on studies with credible quality. The tools lacked factorial and predictive validity, and standardized norms. Further refinement of the existing tools is needed, particularly in the domains of content validity and consequential validity. The synthesized validity evidence and descriptions of the tools reported in this review might guide clinicians and researchers in the selection of an appropriate tool.