Mary Dinsmore Ainsworth (née Salter) was an American-Canadian developmental psychologist known for her work in the development of the attachment theory. She designed the strange situation procedure to observe early emotional attachment between a child and their primary caregiver.
This is an important book regarding attachment theory. Ainsworth follows Bowlby in grounding Attachment Theory. Her introduction of The Strange Situation details how this research was developed. This is not an easy to read book and would not be one that I would recommend as a first book about attachment theory.