The P300 component of the event-related potential (ERP) has been studied extensively in schizophrenia for over 50 years. Initially described in 1965, the P300 reflects cognitive processes and is elicited even when a stimulus is omitted. It was later recognized as an electrophysiological measure that could be used in cognitive psychology to study diseases like schizophrenia. Early studies showed reduced P300 amplitudes in schizophrenia compared to healthy individuals, and this finding has been consistently replicated over the years. Auditory P300 is more likely to be reduced than visual P300 in schizophrenia. P300 amplitude reductions are considered a stable trait marker of the illness, but they can also vary with clinical state and illness duration. Recent research has expanded the understanding of P300 beyond its role in schizophrenia itself, exploring its potential as a biomarker for clinical or genetic vulnerability to psychosis. Studies of individuals at clinical high risk for psychosis (CHR-P) have shown reduced P300 amplitudes, with some findings suggesting that P300 deficits in CHR-P individuals are similar in magnitude to those in schizophrenia patients. Longitudinal studies have shown that P300 amplitudes may predict future psychosis onset and clinical outcomes in CHR-P individuals. P300 research has also explored its relationship with cognitive functions and genetic factors. Twin and family studies have indicated that P300 abnormalities have a heritable component, with heritability estimates ranging from 68-80% for P300 amplitude and 21-56% for P300 latency. Genetic studies have linked P300 abnormalities to specific genes, such as DISC1 and COMT, and to disrupted genetic markers associated with schizophrenia. However, replication of these findings remains a challenge. In addition, P300 research has explored its relationship with neurotransmitter systems, including NMDAR, noradrenergic, dopaminergic, and GABAergic systems. Pharmacological challenge studies have shown that NMDAR hypofunction may contribute to P300 abnormalities in schizophrenia. These findings suggest that P300 may be a useful biomarker for understanding the biological mechanisms underlying schizophrenia and for developing targeted treatments. Overall, P300 research has provided valuable insights into the cognitive and biological mechanisms of schizophrenia, and its potential as a biomarker for clinical and genetic vulnerability to psychosis. Future research should focus on expanding the use of P300 in schizophrenia research, including the development of more nuanced models of P300 generation and its relationship with cognitive functions and treatment outcomes.The P300 component of the event-related potential (ERP) has been studied extensively in schizophrenia for over 50 years. Initially described in 1965, the P300 reflects cognitive processes and is elicited even when a stimulus is omitted. It was later recognized as an electrophysiological measure that could be used in cognitive psychology to study diseases like schizophrenia. Early studies showed reduced P300 amplitudes in schizophrenia compared to healthy individuals, and this finding has been consistently replicated over the years. Auditory P300 is more likely to be reduced than visual P300 in schizophrenia. P300 amplitude reductions are considered a stable trait marker of the illness, but they can also vary with clinical state and illness duration. Recent research has expanded the understanding of P300 beyond its role in schizophrenia itself, exploring its potential as a biomarker for clinical or genetic vulnerability to psychosis. Studies of individuals at clinical high risk for psychosis (CHR-P) have shown reduced P300 amplitudes, with some findings suggesting that P300 deficits in CHR-P individuals are similar in magnitude to those in schizophrenia patients. Longitudinal studies have shown that P300 amplitudes may predict future psychosis onset and clinical outcomes in CHR-P individuals. P300 research has also explored its relationship with cognitive functions and genetic factors. Twin and family studies have indicated that P300 abnormalities have a heritable component, with heritability estimates ranging from 68-80% for P300 amplitude and 21-56% for P300 latency. Genetic studies have linked P300 abnormalities to specific genes, such as DISC1 and COMT, and to disrupted genetic markers associated with schizophrenia. However, replication of these findings remains a challenge. In addition, P300 research has explored its relationship with neurotransmitter systems, including NMDAR, noradrenergic, dopaminergic, and GABAergic systems. Pharmacological challenge studies have shown that NMDAR hypofunction may contribute to P300 abnormalities in schizophrenia. These findings suggest that P300 may be a useful biomarker for understanding the biological mechanisms underlying schizophrenia and for developing targeted treatments. Overall, P300 research has provided valuable insights into the cognitive and biological mechanisms of schizophrenia, and its potential as a biomarker for clinical and genetic vulnerability to psychosis. Future research should focus on expanding the use of P300 in schizophrenia research, including the development of more nuanced models of P300 generation and its relationship with cognitive functions and treatment outcomes.