Erikson's Psychosocial Theory outlines 8 stages of psychosocial development from infancy to late adulthood. Each stage presents a developmental crisis centered around trust, autonomy, initiative, industry, identity, intimacy, generativity, and integrity. Successful completion of each prior stage is important for healthy development. Challenges not met may resurface later. Mastery is not required to advance but can be modified by later experiences. The theory emphasizes the importance of social experience throughout development.