**Abstract** There has been a significant increase in research into compassion with investigation into the neural correlates of compassion and the development of compassion training programs. Yet there is still a lack of agreement over definitions of compassion and what are its core elements. This impacts on the rigour of compassion research. There is broad consensus that compassion is a concern when confronted with another’s suffering and a desire to alleviate that suffering. However, some conceptualisations of compassion vary significantly from this consensus view. Compassion is considered a virtue, it recognises the inherent worth and dignity of all humans, and is often the core value of hospitals, schools and charities. Compassion acknowledges the universality of suffering, that all humans seek happiness and do not wish to suffer. The perception of common humanity has been suggested by several authors to be the central component of compassion. A critical review of the literature suggests that compassion has 5 key elements: (i) compassion is a concern regarding the suffering of another and a desire to alleviate that suffering; (ii) compassion is focused on the other, it does not contain self-reference elements; (iii) compassion arises in response to an identification with a common humanity; (iv) compassion is a motivation, it does not inherently include action; (v) compassion is a process of appraisals. The Sequential-Relational Model of Compassion is proposed to capture the core appraisals of compassion and illustrate the complex array of factors required for compassion to come into being.