The goal of this research was to develop and validate an instrument designed to measure the three types of self proposed by Hodgins and Knee (2002): integrated, ego-invested, and impersonal. This measure was termed The Ego Functioning Questionnaire (EFQ). In Study 1 (N=202), the factorial structure of the EFQ was examined by means of an exploratory factor analysis, and the metric properties of its subscales were documented. In Study 2 (N=300), the 3 factor structure of the EFQ was successfully corroborated using a confirmatory factor analysis. In Study 3 (N=131), associations between the EFQ and a variety of cognitive, affective, and social variables were found to display meaningful patterns, thereby providing support for the EFQ’s construct validity. Also, the EFQ was not susceptible to socially desirable responding. Results are discussed in terms of their fundamental and applied implications.