The ways in which individuals cope with stress has been the subject of much psychological research. Traditionally, coping has been understood as either a disposition, implying stability of individual coping style across situations, or as a process involving individual appraisal of situations and resources, leading to use of a variety of coping strategies. There is considerable evidence of maladaptive psychological and physical health outcomes in relation to different coping styles. More recent research suggests that flexibility in choice of coping response may be more adaptive than any particular style or strategy. The concept of coping adaptiveness, as measured by the Personal Functioning Inventory (PFI), is a relatively recent addition to the stress and coping literature. It emphasises the importance of accurate judgement of the controllability of the stressor in the coping process, as well as sufficient determination and self-control to ensure the most adaptive coping response when faced with obstacles or pressures to respond otherwise. The concept of discriminative facility has been shown to be a useful predictor of individual appraisal of controllability, and in the absence of scales designed specifically to measure determination and self-control, it is proposed in the present study that discriminative facility, general self-efficacy (which may be similar or related to determination), and mindfulness (which may help an individual have greater control over their responses), may be related to coping adaptiveness. Further predictions are that coping adaptiveness is negatively related to psychological distress, and positively with psychological wellbeing, and that coping adaptiveness mediates the proposed predictive relationships between general self-efficacy and mindfulness with psychological wellbeing. In a cross sectional design, 37 participants from a primary care adult clinical population, experiencing a variety of stress and mood related difficulties (study 1), and 159 undergraduate students and nonclinical associates of the researcher (study 2) took part in this study, by completing standardised questionnaires. The results of correlational analysis broadly supported associations in the theoretically predicted directions, and mediational analysis in study 2 suggested a significant mediation effect of coping adaptiveness in the relationship between mindfulness and psychological wellbeing, and general self-efficacy and psychological wellbeing in the nonclinical sample. Results from both studies are discussed in relation to methodological, theoretical and clinical implications.