Fear is a primary emotion that is experienced in the moment, elicited by signs of danger in the world. Infants’ positive and negative emotions to novelty were explored in a number of classic experiments that set up challenges that might provoke fear or more positive reactions from infants. Early signs of fear are also measured using the ‘visual cliff.’ The idea that ‘fear of separation’ is a normal developmental milestone is paralleled by the similar idea that infants become naturally afraid of strangers shortly before their first birthday, the time when they are developing focused attachment relationships with their caregivers. Fears are related to the growth of children’s imaginations, as shown in their expressed fears of imaginary beings like ghosts and monsters. Some children worry more than others, and excessive levels of worry are often shown by children with clinically significant anxiety disorders. The women with anxiety disorders were less likely than other women to engage in easy conversation with the stranger.