Abstract
John Bowlby's attachment theory has made a lasting contribution to scientific understanding of the nature and the impact of close interpersonal bonds, tracing their influence from early childhood through adulthood and into bereavement. The experience of separation and loss featured powerfully in Bowlby's account of the causes of mental health difficulties. He acknowledged many sources for his ideas. However, one potential intellectual force, namely, that of the eminent philosopher Bertrand Russell, is missing. The association between Bowlby and Russell is highlighted in this essay to illustrate how a monumental theory may emerge from ideas already around during a particular historical period. Scientific and personal features of their lives are explored to shed light on possible influence. Commonalities between their propositions about attachment are described as well as pertinent biographical details. Questions whether Bowlby was aware of Russell's writing on this topic and reasons why Russell's ideas were not acknowledged are considered.