Parent-infant attachment is an affectional bond between a young child and his mother. However, the interactions between developmentally delay children and their parents are limited by children's cognitive ability and motor function. If parents understand the concept of parent-infant attachment, they can assist such an attachment becomes formed and that later serves to mediate the parent-infant relationship. This paper clearly points out the definition of attachment, defining attributes (proximity, reciprocity, and commitment) and characteristics, antecedents and consequences, empirical referent, and application the concept of attachment in the relationships between developmentally delay children and their parents.