This selection of key lectures by John Bowlby includes the long and important one that gives the volume its title. Informed by wide clinical experience, and written with the author's well known humanity and lucidity, taken together, the lectures provide an invaluable introduction to John Bowlby's thought and work. In addition to the basic principles with which they are mainly concerned, they also contain much practical guidance of use both to parents and to members of the mental health professions.