Mary Ainsworth

American-Canadian developmental psychologist who extended John Bowlby's attachment theory into a testable research program. After observational fieldwork on mother-infant pairs in Uganda and then in Baltimore, Ainsworth designed the Strange Situation, a standardized laboratory procedure that classified infant attachment as secure, insecure-avoidant, or insecure-resistant from how a child used its mother as a secure base across brief separations and reunions. Published in full with Blehar, Waters, and Wall as Patterns of Attachment (1978), the procedure remains the standard instrument for attachment research and shaped decades of work on early caregiving and child development.