The attachment theory, which was developed half a century ago by a British psychiatrist and psychoanalyst, John Bowlby, is the most fundamental theory for raising infants and children. His colleagues, Mary Ainsworth and James Robertson, contributed to proving Bowlby's theory with scientific ways. Many neo-Bowlbyans continue to apply theories for raising children and also for use in clinical practices. Attachment refers to the process by which people develop specific, positive emotional bonds with others. When suitably formed, people want to keep proximity with an attached object, feel safety from the object as a secure base, and resist when separated. In general, attachment has developed between infants and caregivers, mainly mothers. It usually continues till adulthood and sometimes until the next generation. Attachment is an individual affectional bond, and also can be an influential factor to decide the social policies of related realms. Therefore, the attachment theory provides very useful knowledge for child rearing parents, very practical data for doctors and allied professionals, and also very important decision framework for social policy makers.