In recognition of the broad influence of attachment theory, the articles in this issue cut across diverse areas of psychology and multiple levels of analysis. T. R. Insel (2000) focuses on the molecular level, discussing the complex link between neurobiology and attachment behavior in nonhuman animals. The three articles by J. Cassidy (2000), R. C. Fraley and P. R. Shaver (2000), and P. R. Pietromonaco and L. Feldman Barrett (2000) present midlevel analyses, incorporating ideas about the links between mental representations and relationship thoughts, feelings, and behavior. C. Hazan and L. M. Diamond (2000) take a macro approach by applying a broad evolutionary perspective to understand the basis for attachment in adult pair bonds. The discussion focuses on unifying themes, including the interplay between attachment, caregiving, and sexual behavior; attachment functions in adult relationships; evolutionary processes; the operation of internal working models; and continuity in attachment across the life span.