Following the publication of Karl Jaspers’ General Psychopathology (1913), delusions have been characterized as being nonunderstandable in terms of the person’s biography, motivations, and historical-cultural context. According to Jaspers, this loss of understandability is due to an underlying neurobiological process, which has interrupted the normal development of the individual’s personality. Inheriting the 19th-century division between the natural- and human-historical sciences, Jaspers emphasizes the psychological understanding of mental disorders as narrative-based, holistic, and contextual. By doing so, he embraces cultural, ethnic, and individual differences and anticipates a person-centered medicine. However, he also affirms the value of explanatory neurobiological approaches, especially in the research and diagnosis of delusions. The phenomenological approach leads to neurobiological hypotheses, which can be tested experimentally. The present article addresses these issues by illustrating Jaspers’ fundamental contribution to current neurobiological research concerning the formation of delusions during early phases of psychosis. Specifically, we present delusional mood and Truman symptoms as core phenomenological features at the origin of psychosis onset, and we discuss their neurobiological substrate with the aberrant salience and dopamine dysregulation models. Jaspers and his successors’ phenomenological approach suggests that delusion is formed through loss of context in its experiential-perceptual origins. This is consistent with the more recent neurobiological models.