Interactions between newborns and their parents/primary caregivers are characterized by asymmetric and dependent relationships. This systematic review mapped, identified, and described the psychometric parameters, categories, and items of instruments used to assess mother-newborn interaction. Seven electronic databases were accessed in this study. Furthermore, this research included neonatal interaction studies describing instruments' items, domains, and psychometric properties while excluding studies that focused on maternal interactions and lacked items for assessing newborns. Additionally, studies validated with older infants that did not have a newborn in the sample were used for test validation, which is a criterion used to decrease the risk of bias. Fourteen observational instruments from 1047 identified citations were included that addressed interactions using varying techniques, constructs, and settings. Particularly, we focused on observational settings that assessed interactions with communication-based constructs in the context of proximity or distance as influenced by physical, behavioral, or procedural barriers. These tools are also used to predict risk behaviors in a psychological context, mitigate feeding difficulties, and conduct neurobehavioral assessments of mother-newborn interactions. The elicited imitation was also an observational setting. This study found that the most described properties in the included citations were inter-rater reliability followed by criterion validity. However, only two instruments reported content, construct, and criterion validity, as well as a description of an internal consistency assessment and inter-rater reliability. Finally, the synthesis of the instruments reported in this study can guide clinicians and researchers in selecting the most appropriate one for their own application.