As I stated in the previous chapter, the third phase of attachment theory has emerged the 1990s, with a series of experimental, theoretical, and clinical studies by Peter Fonagy, Miriam Steele, and Howard Steele at University College London, and Mary Main and colleagues in the USA. They have developed and used the adult attachment interview (AAI) to categorise the state of mind of parents-to-be regarding the ways in which they tend to make and sustain important attachments in their lives. They have then used this to compare the subsequent attachment classification of the infant born to them, by classifying that infant’s attachment schema using the strange situation test that Mary Ainsworth first devised (Fonagy et al., 2002).