The P300 event-related brain potential (ERP) is a key component in cognitive electrophysiology, reflecting attention and memory processes. This review integrates empirical and theoretical findings to clarify the P300's characteristics, origins, and functions. The P300 is composed of two subcomponents, P3a and P3b. P3a is associated with stimulus-driven frontal attention mechanisms during task processing, while P3b is linked to temporal-parietal activity related to attention and subsequent memory processing. Neurotransmitter actions, such as dopaminergic pathways for P3a and norepinephrine pathways for P3b, are highlighted. Neuroinhibition is proposed as an overarching mechanism for P300, which is elicited when stimulus detection engages memory operations. The P300's amplitude and latency are influenced by factors such as stimulus probability, task difficulty, and individual differences in cognitive function. P300 amplitude is sensitive to attentional resource allocation and memory load, with larger amplitudes observed for tasks requiring more attention. P300 latency is related to classification speed and is affected by task processing demands. Individual differences in P300 latency correlate with mental function speed, with shorter latencies indicating superior cognitive performance. The P300 is also influenced by genetic factors and personality traits. Genetic studies suggest that P300 is heritable, with variations in ERP characteristics linked to specific loci on the human genome. Personality-related arousal levels are associated with P300 amplitude, with high-arousal individuals showing larger amplitudes. The P300's neuropharmacological basis is discussed, with the dual-transmitter hypothesis suggesting that P3a is related to dopaminergic activity and P3b to norepinephrine pathways. Neuropharmacological studies in humans indicate that dopaminergic activity affects P3a and some portion of P3b. The neuropsychological origins of P3a and P3b are explored, with findings suggesting that these components are variations of the same generation system. P3a is associated with frontal attention mechanisms, while P3b is linked to temporal-parietal areas involved in memory processing. The neural generators of P300 are discussed, with frontal lobe integrity necessary for P3a generation and parietal lobe integrity affecting P3b. The P300 is generated through a circuit pathway between frontal and temporal/parietal brain areas. The P300's function is discussed, with the inhibition hypothesis suggesting that P300 reflects rapid neural inhibition of ongoing activity to facilitate transmission of stimulus/task information. The P300 is generated in the service of memory storage, with findings supporting this view. Neuroelectric and neuroimaging studies suggest that P300 is associated with attention and memory processes, with functional and structural imaging data mimicking the neuroelectric morphThe P300 event-related brain potential (ERP) is a key component in cognitive electrophysiology, reflecting attention and memory processes. This review integrates empirical and theoretical findings to clarify the P300's characteristics, origins, and functions. The P300 is composed of two subcomponents, P3a and P3b. P3a is associated with stimulus-driven frontal attention mechanisms during task processing, while P3b is linked to temporal-parietal activity related to attention and subsequent memory processing. Neurotransmitter actions, such as dopaminergic pathways for P3a and norepinephrine pathways for P3b, are highlighted. Neuroinhibition is proposed as an overarching mechanism for P300, which is elicited when stimulus detection engages memory operations. The P300's amplitude and latency are influenced by factors such as stimulus probability, task difficulty, and individual differences in cognitive function. P300 amplitude is sensitive to attentional resource allocation and memory load, with larger amplitudes observed for tasks requiring more attention. P300 latency is related to classification speed and is affected by task processing demands. Individual differences in P300 latency correlate with mental function speed, with shorter latencies indicating superior cognitive performance. The P300 is also influenced by genetic factors and personality traits. Genetic studies suggest that P300 is heritable, with variations in ERP characteristics linked to specific loci on the human genome. Personality-related arousal levels are associated with P300 amplitude, with high-arousal individuals showing larger amplitudes. The P300's neuropharmacological basis is discussed, with the dual-transmitter hypothesis suggesting that P3a is related to dopaminergic activity and P3b to norepinephrine pathways. Neuropharmacological studies in humans indicate that dopaminergic activity affects P3a and some portion of P3b. The neuropsychological origins of P3a and P3b are explored, with findings suggesting that these components are variations of the same generation system. P3a is associated with frontal attention mechanisms, while P3b is linked to temporal-parietal areas involved in memory processing. The neural generators of P300 are discussed, with frontal lobe integrity necessary for P3a generation and parietal lobe integrity affecting P3b. The P300 is generated through a circuit pathway between frontal and temporal/parietal brain areas. The P300's function is discussed, with the inhibition hypothesis suggesting that P300 reflects rapid neural inhibition of ongoing activity to facilitate transmission of stimulus/task information. The P300 is generated in the service of memory storage, with findings supporting this view. Neuroelectric and neuroimaging studies suggest that P300 is associated with attention and memory processes, with functional and structural imaging data mimicking the neuroelectric morph