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The recently proposed Suicidal Drive Hypothesis challenges traditional perspectives regarding the relationship between suicidality and psychosis. It proposes a bidirectional framework in which suicidality may operate as a risk factor for, as well as an outcome of psychosis. Rooted within a context of threat responsivity, the hypothesis considers suicidality as an internally generated and self-directed threat and psychosis as an adaptive strategy which externalises this threat. Given encouraging preliminary evidence demonstrating suicidality – psychosis directionality the current thesis sought to explore the conceptualisation of internal threat, more broadly beyond suicidality, and to examine how psychosis varies in relation to it. A novel continuum of internal threat was modelled using data from the British Psychiatric Morbidity Survey (N = 8580). Exploratory and confirmatory factor analyses identified a correlated 4-factor structure of internal threat (low self-worth and subordination, depression, suicidal thoughts and self-harm) while subsequent factor mixture modelling revealed seven classes that in turn reflected graded levels of internal threat severity. Traumatic experiences and markers of social adversity conferred risk for class membership. Graded classes of internal threat severity were also modelled in separate population-based samples from the UK and Israel, using symptoms derived from established external threat (trauma)-related psychiatric phenomena (Complex PTSD and Borderline Personality Disorder) which, notably, have been meaningfully associated with psychosis. While clinical psychotic disorder status was associated mainly with extreme expressions of internal threat (i.e. suicidality), subclinical psychotic experiences (PEs) were associated with internal threat across the continuum from lower to more extreme levels. Furthermore, examination of PE connectivity at different levels of internal threat severity suggested an ‘evolving’ and ‘growing’ network of internal threat oriented psychosis. This thesis not only advances the Suicidal Drive Hypothesis but also introduces a broader conceptualisation of internal threat that may have applications beyond psychosis research. A broad array of clinical, theoretical and methodological implications of this research are considered throughout.