A theory decomposing volition into four modes of central organization of executive control functions is outlined. These modes include (1) an autonomy-oriented mode (“self-regulation”) which is facilitated by challenging conditions and positive mood, (2) a self-suppressive mode oriented toward external-control (“self-control”) facilitated by negative mood and two modes associated with volitional inhibition (“state orientation”). Two experiments are reported that test predicted interactions between dispositional and situational factors in determining commitment to and actual enactment of self-chosen versus assigned activities directed at changing nutritional behavior. The results confirm the predicted disordinal interactions: The degree of commitment to and enactment of intended behavioral changes depends upon an interaction between personality (volitional styles), type of self-regulatory task (eat more healthy versus avoid unhealthy food), and instructional focus on easy versus difficult steps (Study 1) or self-reward versus self-punishment strategies (Study 2). Practical implications for designing intervention procedures according to individual personality characteristics and situational constraints are discussed.