Aphantasia and hyperphantasia refer to extreme variations in the vividness of mental imagery. Aphantasia is the absence or near-absence of conscious, wakeful imagery, while hyperphantasia involves imagery as vivid as real perception. Approximately 1% of the population experiences profound aphantasia, and 3% experience hyperphantasia. Aphantasia often runs in families and is associated with reduced autobiographical memory, face recognition difficulty, and autism. Visual dreaming is typically preserved in aphantasia. Hyperphantasia is less studied but appears more common than aphantasia. Both conditions have distinct behavioral, physiological, and neural correlates. Aphantasia is linked to reduced spatial imagery but preserved spatial skills, while hyperphantasia is associated with enhanced visual and spatial imagery. Aphantasia is more common in individuals with mathematical, scientific, or computational careers, while hyperphantasia is more common in creative fields. Aphantasia is associated with reduced autobiographical memory and face recognition, but not with reduced cognitive abilities. Neuroimaging studies suggest that altered connectivity between frontoparietal and visual networks may underlie these extremes. Aphantasia may also be linked to autism, but it does not impair daily functioning. The neural basis of these extremes is still being explored, with some evidence suggesting differences in brain structure and connectivity. Aphantasia is not classified as a disorder but as a neurodiverse variation. Future research aims to clarify the genetic, neural, and behavioral underpinnings of these extremes.Aphantasia and hyperphantasia refer to extreme variations in the vividness of mental imagery. Aphantasia is the absence or near-absence of conscious, wakeful imagery, while hyperphantasia involves imagery as vivid as real perception. Approximately 1% of the population experiences profound aphantasia, and 3% experience hyperphantasia. Aphantasia often runs in families and is associated with reduced autobiographical memory, face recognition difficulty, and autism. Visual dreaming is typically preserved in aphantasia. Hyperphantasia is less studied but appears more common than aphantasia. Both conditions have distinct behavioral, physiological, and neural correlates. Aphantasia is linked to reduced spatial imagery but preserved spatial skills, while hyperphantasia is associated with enhanced visual and spatial imagery. Aphantasia is more common in individuals with mathematical, scientific, or computational careers, while hyperphantasia is more common in creative fields. Aphantasia is associated with reduced autobiographical memory and face recognition, but not with reduced cognitive abilities. Neuroimaging studies suggest that altered connectivity between frontoparietal and visual networks may underlie these extremes. Aphantasia may also be linked to autism, but it does not impair daily functioning. The neural basis of these extremes is still being explored, with some evidence suggesting differences in brain structure and connectivity. Aphantasia is not classified as a disorder but as a neurodiverse variation. Future research aims to clarify the genetic, neural, and behavioral underpinnings of these extremes.