Mindfulness is the process of actively drawing novel distinctions. It results in context-sensitivity and a heightened awareness of alternative perspectives (Langer in Higher stages of human development: Perspectives on adult growth. Oxford University Press, New York, pp. 114–136, 1989). By being “mindful”, one continually draws from the present experiences and creates expanded possibilities (Alexander et al. in Higher stages of human development: Perspectives on adult growth. Oxford University Press, New York, pp. 114–136, 1990). Mindfulness is multifaceted and needs to be examined from multiple perspectives. In order to understand the concept of mindfulness and its application in daily life, it is very important to come to a standard consensus on mindfulness and study it empirically. In the chapter, a series of definitions is given to put mindfulness into a scientific context. The five behavioral components based on or related to behavioral training procedures are identified to understand critical mindfulness. The benefits of cultivating mindfulness in well-being are discussed.