The current thesis aimed to contribute to the conceptualisation of mindfulness in psychology by investigating the differences and similarities in mindfulness between Buddhism and psychology. Mindfulness is the English translation for the Pali word sati in Buddhism, which literally means remembering. Mindfulness is a central element of Mindfulness-Based Interventions (MBIs), in which mindfulness is commonly viewed, among other characteristics, as non-judgmental present-centred awareness. Although there is an agreement in psychology on some characteristics of mindfulness, the field of psychology has not reached a consensus on the nature and the construct of mindfulness. The conceptual unclarity of mindfulness may have hindered progress in identifying the mechanisms of mindfulness by which it exerts health benefits. Study 1 investigated differences in mindfulness between Buddhism and Western psychology by interviewing Buddhists. Five senior clergy from three branches of Buddhism were interviewed for their opinion on the Mindfulness Attention and Awareness Scale (MAAS), Kentucky Inventory of Mindfulness Skills (KIMS), Five Factor Mindfulness Questionnaire (FFMQ), and Freiburg Mindfulness Inventory-30 (FMI-30). The interviewees also rated the questionnaire items for an ideal Buddhist in their tradition, in order to provide a stimulus for discussion and to collect quantitative data along with the qualitative data. Eight themes in relation to the elements and features of Buddhist mindfulness emerged from thematic analysis. The themes indicated that there are considerable differences between Buddhist mindfulness and mindfulness as presented by items in the questionnaires. While mindfulness in psychology is frequently conceptualised as non-judgmental, present-centred awareness, Buddhist mindfulness contains elements of attentional flexibility, skillfulness, purposefulness, wisdom, and ethics. Buddhist mindfulness not only involves awareness of the present but also the past and future. It not only focuses on self but also on others. The quantitative results revealed that the MAAS and the FMI-30 appeared less incongruent with Buddhist mindfulness than the KIMS and the FFMQ. Any differences highlighted in Study 1 provide avenues for future research as aspects unique to Buddhist mindfulness practice may be linked to psychological benefits also in secular contexts, thus assisting efforts to investigate to what extent secularisation of mindfulness practice may have resulted in loss of some potentially beneficial characteristics. Based on the findings of Study 1 and Buddhist theories, Study 2 proposed and tested a model in which non-attachment mediated between three predictor variables (ethics, concentration, and wisdom) and well-being in 546 participants. The results indicated that both ethics and wisdom predicted well-being beyond mindfulness in psychology. Ethics, however, showed weak positive effects on well-being, and became redundant after wisdom was included in the model. Also, the model containing wisdom and concentration had a better model fit than the model including ethics, concentration, and wisdom. This may suggest that ethics was not an important component of mindfulness that contributed to secular well-being. Wisdom, on the other hand, was a strong predictor of non-attachment and well-being in the model. This indicated that wisdom could be extended from Buddhism to secular context, and may be a component of mindfulness that is potentially useful for psychology. As to suitable mediators, non-attachment in Study 2 partially mediated between mindfulness and well-being, which indicated that other mediators likely exist. Although a complete model has not been achieved, Study 2 provided useful information on potential components of mindfulness, and mechanisms of mindfulness.