The purpose of this thesis is to further evolve and clarify the definition of Psychological/Emotional Abuse and Neglect (PEA) of children and consider the implications the definition has for policy, practice, and research. The definition of PEA is examined from multiple perspectives based on a definitional conceptual framework which consists of (i) abuser, (ii) abusive behaviour, (iii) intention, (iv) frequency, (v) interaction, (vi) consequences, (vii) child age, and (viii) child's other characteristics. First, an examination of abstract definitions (i.e. theoretical meaning) of PEA amongst academic and broader literature was conducted. The analysis using the conceptual framework provided a broad picture of PEA definitions and highlighted its nature and diversity. Second, operational definitions (i.e. determining the response threshold) of PEA in guidelines were investigated to identify how general professionals are guided to exercise the definitions. The results identified various thresholds of PEA for different levels of response within as well as across jurisdictions. The study highlighted that operationalisation of PEA is often left open to professionals' own judgement. Third, a systematic review was undertaken of existing primary studies on professionals' PEA definitions. The review demonstrated the high threshold of professionals' abstract definitions (i.e. recognising) as well as operational definitions (i.e. responding) of PEA compared to other types of CAN. Finally, an original vignette survey study, underpinned by the conceptual framework and the findings of previous chapters, was undertaken to examine the current situation of professionals' PEA definitions. The study identified a high threshold for both abstract and operational definitions by the respondents. Importantly, the suspicion of PEA did not always result in professionals' response. Frequency, consequences and abusive behaviour were strong predictors of professionals' definitions of PEA. Overall, the thesis provides a conceptual analysis and data on definition of PEA, draws implications and considers strategies for further research in the area.