Three studies evaluated the reliability and validity of the Investment Model Scale, an instrument designed to measure four constructs, including commitment level and three bases of dependence–satisfaction level, quality of alternatives, and investment size. In all three studies, reliability analyses revealed good internal consistency among items designed to measure each construct. Also, principal components analyses performed on scale items revealed evidence of four factors, with items designed to measure each construct loading on independent factors. Studies 2 and 3 examined associations of model variables with instruments measuring diverse qualities of relationships and assorted personal dispositions. As anticipated, Investment Model variables were moderately associated with other measures reflecting superior couple functioning (e.g., dyadic adjustment, trust level, inclusion of other in the self), and were essentially unrelated to measures assessing personal dispositions (e.g., need for cognition, self‐esteem). In addition, Study 3 demonstrated that earlier measures of Investment Model variables predicted later levels of dyadic adjustment and later relationship status (persisted vs. ended). It is hoped that the existence of a reliable and valid Investment Model Scale will promote further research regarding commitment and interdependence in ongoing close relationships.