Since it was discovered by Aristotle as a feature of mind, not just of language, metaphor has captured the attention of philosophers, scientists, psychologists, semioticians, and others, given its importance to revealing how human thought might unfold. Although ignored for centuries as a mere rhetorical device after Aristotle, metaphor came under the microscope of cognitive scientists already at the start of the twentieth century, leading gradually to conceptual metaphor theory by the end of the 1970s. This entry looks at the history of metaphor study focusing on the latter theory and its two major components—image schemas and idealized cognitive models. Overall, it has become apparent that metaphor cannot be seen simply as a rhetorical speech device but rather as revealing an unconscious form of systematic understanding that reveals, in turn, how the human brain makes connections among things, guided by sensory and affective experiences.