Thomas Harris's I'm OK, You're OK is a self-help book applying transactional analysis (TA) to improve personal relationships. 

TA analyzes interactions and communication patterns using the concepts of parent, adult, and child ego states. The book explores how these ego states influence behaviour in various contexts, such as marriage, parenting, and social interactions. 

Harris emphasizes shifting from unhealthy "life positions" (e.g., "I'm not OK—you're OK") to a healthier "I'm OK—you're OK" position through self-awareness and improved communication. The book includes clinical examples and case studies illustrating TA's practical applications.