BACKGROUND: Empirical research has been produced on the topic of 'Internet Addiction' or 'Problematic Internet Use' (PIU) for more than 20 years, with a variety of theoretical approaches suggested by scholars to account for the behaviour. However, the discourse has been fraught with debate around construct definition, measurement, and validity.

AIMS: This review aimed to systematically review the extant literature on the topic of PIU, to identify the published psychological theories in the area, and to synthesise the findings to produce actionable information for practicing psychologists as well as academics.

METHOD: Given the breadth of the aims, a scoping review methodology was utilised. Four major reference libraries (Scopus, Proquest, Pubmed, Technology Research Database) were searched using a string of relevant terms.

RESULTS: Of 1412 initial search results, eighteen theories were included in the study. Nine theories related to generalised PIU, seven related to specific Internet use issues, such as online gaming or social media, while two theories took account of both a generalised and specific view. Data were analysed using Formulation-Based Thematic Analysis (FBTA) to synthesise theory elements under the deductive headings of Predisposing, Precipitating, Maintaining, and Protective factors.

DISCUSSION: The lack of protective factors against PIU was a prominent finding. The utility of the psychological formulation approach, particularly in an area fraught with conceptual debate and frustration with traditional medical classification systems, is emphasised.