The theory of reasoned action (TRA;Fishbein & Ajzen, 1975), the theory of planned behavior (TPB; Ajzen, 1985) and the theory of self-regulation (TSR; Bagozzi, 1992) were applied to Italian undergraduate students' studying behavior. The main focus of the research was to ascertain the predictive power of past behavior on intention and behavior and thus test for the suciency of the theories. For theory suciency to be demonstrated, past behavior in¯uences on intention and present behavior should be totally mediated by the focal variables of the theories (attitudes, subjective norms, perceived behavioral control and desire). It is argued that past behavior aects intentions and present behavior over and above attitudinal variables and that these eects will be weaker on intention for the TPB and TSR models. A structural equation approach was used to test the construct validity of measures such as the predictive validity of the theories. A total sample of 240 Italian college students participated in the research. A subsample of 90 subjects provided a self-report behavioral measure one week later. Results show that past behavior is a strong predictor of both intention and behavior in the TRA model, while it is a weaker predictor of intention in the TPB and in the TSR models. Implications for attitude± behavior relationships are discussed.