Background and Objectives: Poor insight or impaired awareness of illness is a very common feature in psychosis. The purpose of this study is to review critically the conceptual approximations from different perspectives to insight in psychosis and address its relations to other clinical and psychopathological variables. Methods: We reviewed the principal factors that have been proposed to contribute to deficient insight in first episode psychosis patients from different conceptual frameworks, defence mechanisms or coping styles, structural or volumetric brain associations, cognitive deficits, and severity of clinical symptoms. Results: This review of literature suggests that insight is a complex mental faculty heavily influenced by additional factors, such as social and cultural aspects, among others. Results also show the correlates of insight in first episode psychosis and treatment adherence in the course of the illness, although it is not stable over time. In fact, adequate level of insight is a necessary, but not sufficient condition for an adequate adherence. Conclusions: Insight is a complex and multidimensional mental faculty that is a key factor in the prognosis of the illness. The link between both is probably mediated by the interaction of additional variables such as DUP, affective symptoms, sociodemographics, and drug abuse. Due to the complex relationships among insight, cognition and psychopathology in psychosis, these three factors could be considered as semi-independent phenomena. Finally, the neuroscience perspective about insight in psychosis is an especially productive research line that has contributed to a better understanding of the complex picture.