Psychological vocabulary has been studied in developmental subjects with both typical and atypical development and in their caregivers through the analysis of metacognitive vocabulary and the assessment of mental verb comprehension, as well as through the observation of spontaneous language. Mental language has been assessed in relation to various conceptual domains and in different cultures and its relationships with mentalistic skills have been highlighted. The role of culture in the construction of language to talk about the mind has been highlighted by the study of childhood narratives in different cultures as sources of knowledge about mental states. Maternal mental language in situations of pretend play of mother-child dyads and in “reality” situations (i.e. in mother-child interactions in the absence of pretense) has been studied with a longitudinal methodology.