Diamond's research focuses on two distinct but related areas -- the nature and development of affectional bonds and the nature and development of same-sex sexuality. The common thread uniting these lines of research is my interest in the psychological and biobehavioral processes underlying intimate relationships and their influence on emotional experience and functioning over the life course.

Her primary research questions are as follows: (1) what are the basic psychological and biobehavioral processes underlying the formation and functioning of affectional bonds; (2) how are these processes related to sexual desire and sexual orientation; (3) what are the implications of affectional bonding for mental and physical well-being at different stages of life? In addressing these questions, she uses a diverse range of research methods, including in-depth qualitative interviews, controlled social-psychophysiological experiments, and assessment of naturalistic interpersonal behavior.