Compassion is a multifaceted capacity that involves sensitivity to the suffering of others and motivation to alleviate it. While it is central to many contemplative and religious traditions, it has also gained traction in psychological science. Existing conceptions of compassion include affective, cognitive, and motivational components. Nevertheless, scientific research has been hampered by the absence of a unifying definition and appropriate measurement instruments. This chapter describes a series of studies undertaken to develop the Sussex-Oxford Compassion Scales (SOCS), designed to provide a valid and reliable tool for assessing compassion for both self and others. The first phase involves creating a set of items based on a comprehensive five-element conceptual framework of compassion derived from the literature. The five-element definition of compassion includes the following: (1) recognizing suffering; (2) understanding the universality of suffering in human experience; (3) emotional resonance with the person suffering; (4) tolerating uncomfortable feelings; and (5) acting or feeling motivated to act to alleviate suffering. These items were reviewed and revised using expert consultation and a two-phase item reduction procedure, resulting in a 20-item measure of both self-compassion (SOCS-S) and other-compassion (SOCS-O). Confirmatory factor studies of two diverse populations revealed strong psychometric features and supported a hierarchical five-factor structure for both scales. The final versions of the SOCS-S and SOCS-O showed good internal consistency and validity, with significant correlations to recognized compassion and empathy measures, as well as mental health outcomes.