The article explores the extremes of visual imagery vividness, focusing on aphantasia and hyperphantasia. Aphantasia, affecting about 1% of the population, is characterized by a marked reduction or absence of conscious, wakeful imagery. Hyperphantasia, affecting about 3% of the population, is marked by vivid imagery akin to real seeing. These conditions run in families, often affecting multiple sensory modalities, and are associated with reduced autobiographical memory, face recognition difficulty, and autism. Visual dreaming is typically preserved in aphantasia. Subtypes of extreme imagery exist but are not well defined. Initial studies suggest that alterations in connectivity between frontoparietal and visual networks may underlie these extremes. The article reviews the nature and mechanisms of visual imagery, its prevalence, subjective reports, objective correlates, associations with other conditions, and potential neural bases. It highlights the importance of understanding these extremes for insights into the interrelationships between imagery, perception, memory, neurodevelopment, and mental health.The article explores the extremes of visual imagery vividness, focusing on aphantasia and hyperphantasia. Aphantasia, affecting about 1% of the population, is characterized by a marked reduction or absence of conscious, wakeful imagery. Hyperphantasia, affecting about 3% of the population, is marked by vivid imagery akin to real seeing. These conditions run in families, often affecting multiple sensory modalities, and are associated with reduced autobiographical memory, face recognition difficulty, and autism. Visual dreaming is typically preserved in aphantasia. Subtypes of extreme imagery exist but are not well defined. Initial studies suggest that alterations in connectivity between frontoparietal and visual networks may underlie these extremes. The article reviews the nature and mechanisms of visual imagery, its prevalence, subjective reports, objective correlates, associations with other conditions, and potential neural bases. It highlights the importance of understanding these extremes for insights into the interrelationships between imagery, perception, memory, neurodevelopment, and mental health.