Three studies examine the psychometric properties (i.e., the test-retest reliability, convergent, and discriminant validity) of Fraley, Waller, and Brennan’s Revised Experiences in Close Relationships (ECR-R) self-report measure of romantic attachment anxiety (model of self) and avoidance (model of others). Longitudinal analyses suggest that the ECR-R provided highly stable indicators of latent attachment during a 3-week period (85% shared variance). Hierarchical linear modeling analyses further validated the ECR-R, suggesting that it explained between 30% to 40% of the between-person variation in social interaction diary ratings of attachment-related emotions experienced during interactions with a romantic partner and only 5% to 15% of that in interactions with family and friends. Guidelines are offered regarding the conditions where highly reliable and precise measures of romantic attachment, such as the ECR-R, are deemed necessary and where shorter, albeit slightly less reliable measures, such as Bartholomew and Horowitz’s Relationship Questionnaire, may also be viable.