The "Strange Situation”-(SS)-the principal procedure of assessing infants` attachment patterns is developed by the psychologist Mary Ainsworth in 1978.This procedure observes the behavior of infants in four situations. The mother and the baby are in an experimental room, that would attract baby`s interest. The first feature observed in the experiment is the babies behavior, while the mother is present, after that a strange woman enters and the mother leaves-baby`s behavior towards the stranger is observed, then the baby is left alone in the room-the reaction in this situation is also very important and finally the mother returns and baby`s behavior during reunion is observed. Using this procedure Ainsworth found three main types of attachment, and in  1990 Main and Solomon identified the fourth. The firs one by Ainsworth is insecure-avoidant, known as Type A, secure attachment, known as Type B and insecure-rejecting ,known as Type C and disorganized known as type D. In the first type the baby is avoidant of the mother and is not very distressed when mother is absent. The second type baby uses the mother as a secure base from which to explore the world and shows distress of mother`s absence and is easily calmed when mother returns. The third type is also known  as insecure -ambivalent type, because their orientation towards the mother is highly ambivalent. The last type is vey uncommon and the babies in this category  seem to be disorganized in the situation  and unable to cope with distress. These are the four universal categories in which babies from all over the world may fit. The study of Ainsworth is important not only to classify baby`s attachment types, but also to predict some future behavior development of the child regarding its attachment type.