Attachment instability refers to the process by which people's beliefs, feelings, and behaviors regarding security in relationships change over time. Some people experience a constant feeling of safety and security in close relationships, others experience a constant feeling of insecurity in relationships, and still others experience marked changes in feelings of security over time. The goal of this study is to identify who these latter people are and why their beliefs and feelings are so unstable. The study tests a series of competing hypotheses regarding the extent to which these people are (a) prone to such instability because of early deficits in the development of a positive, coherent sense of self or (b) prone to such deficits because of ongoing changing life circumstances, or (c) some combination of the two. The present study focuses especially on young people, with the goal of identifying those who may be at risk for developing chronic maladaptive interpersonal patterns that put them at continued risk for negative outcomes.