This paper presents the basic foundations of the theory of attachment and its connection with jealousy in romantic relationships. Attachment style can be divided into secure and insecure attachment style and insecure attachment style can also be divided into preoccupied style, dismissive style and fearful style. The basic postulate of theory of attachment is that once formed attachment model remain stable throughout the life of an individual and affects all other close relationships including relationships with partner, friends, family members and so on (Kamenov et al., 2014). Most of the research has been focused on how attachment determines romantic relationships in adulthood. However, some studies have shown that attachment can change throughout life, which means that a person can develop different styles of attachment in different close relationships (Ajduković et al., 2006). Attachment behavior is triggered when an individual is in stressful situation and feels endangered. Jealousy also occurs in situations where an individual is threatened and fears that he will lose relationship with his partner (most often because of a third person). Research has shown that individuals with insecure attachment are more likely to express more jealousy than individuals with secure attachment (e. g. Guerrero, 1998.; Marshall et ali., 2013; Selterman i Maier, 2013)