John Bowlby developed attachment theory to explain connections between infant and caregiver behavior and how these impacted children’s behavior. Extended and researched heavily in a variety of contexts, attachment theory has advanced clinical thinking over time. Its core ideas regarding infant and caregiver connections are very useful to mental health practitioners today and have particular ramifications for clinical work with adults. This paper discusses the application of Bowlby’s attachment theory to the clinical treatment of adult depression and explores a relevant case example.