This chapter aims to develop an expansive understanding of equanimity (Samatva) as a distinct psychological construct. Most of the research on well-being in India has been influenced by Western models. However, to have a clear understanding of what constitutes a happy, content and meaningful life, we need to understand well-being in our cultural context instead of relying on the Western lens of well-being. The concept of equanimity rooted in the indigenous schools of thought such as Hinduism and Buddhism can enrich the theories of Psychology and help cope with the various complexities and uncertainties of life. Recent studies have also stressed that the concepts of mindfulness and equanimity may be conflated in the literature and have emphasised a need to clearly distinguish between the two concepts. Thus, the aim of this chapter is to develop an expansive understanding of equanimity as a distinct psychological construct. To explore equanimity from its roots, the chapter first traces the construct of equanimity as delineated in the Bhagavad Gita and in Buddhist philosophy. Following which, the various theoretical frameworks of equanimity in the psychological literature are then reviewed and outlined. The key psychological processes related to equanimity such as acceptance, experiential avoidance, cognitive reactivity and insight into the nature of phenomena are then elaborated. Following this, the theoretical distinctions between equanimity and mindfulness are outlined. The existing scales and self-report measures of equanimity in the psychological literature are reviewed and critiqued. Following this, the relation between compassion and equanimity is highlighted along with a discussion on the challenges faced in the cultivation of equanimity. The various psychosocial health correlates of equanimity such as well-being, resilience, neuroticism, loneliness and social media addiction are discussed. The implications of the cultivation of equanimity have been discussed for holistic well-being, and indigenous therapeutic and leadership practices, and adaptive coping in crisis situations. As a whole, the chapter provides a platform for conceptual validation of equanimity as a psychological construct with all possible future applications.