Strange situation theory, developed by Mary Ainsworth, is a methodology for studying attachment patterns between infants and caregivers through a series of separations and reunions. It classifies infants into four attachment styles: secure, insecure-avoidant, insecure-resistant, and disorganized. However, the theory faces criticisms regarding cultural diversity, age range applicability, observer bias, limited caregiver assessment, and lack of contextual factors consideration, despite its usefulness in developing interventions aimed at improving attachment.