Frank van der Horst earned his Ph.D. at Leiden University in 2009 and has published widely on the history of attachment theory. His current research at Erasmus University Rotterdam aims at describing the history of ideas in the behavioural sciences, such as the ideas and work of John Bowlby, René Spitz, William Goldfarb, and Harry Harlow. His aim is also to further unravel the roots of attachment theory in, for example, the work of James Robertson and that of developmental psychologist Mary Ainsworth. These studies are necessary to complete our picture of the historical embeddedness of theoretical innovations in (developmental) psychology. Van der Horst is the author of *John Bowlby – From Psychoanalysis to Ethology. Unraveling the Roots of Attachment Theory* (2011) and *Opgroeien in het hedendaagse gezin* (2016). Van der Horst also obtained a Psy.D. while working in forensic psychiatry (and holds Dutch clinical registrations as supervisor NVO, GZ-psychologist and Orthopedagoog-Generalist). Currently, he is training to be a psychotherapist and is involved in graduate and postgraduate clinical supervision.