The authors describe a view that our short-, medium-, and long- term behavior, interactions, and relationships-whether planned or spontaneous, purposeful or playful-can be understood in terms of goal-directed systems. An understanding of action theory and research methods used in applied settings is provided. It leads to the conclusion that individual processes are joint processes and the joint construction of lives should be monitored to understand ongoing personal and social involvements. The unique contribution of this book lies in its bringing together and extending of basic features of the theory of goal-directed action systems previously published in a range of scattered research and conceptual articles in the literature. Professionals including clinicians, counselors, social workers, researchers, doctors, nurses, and physical or occupational therapists will find in this book an accessible means to understand, act on, research, and intervene in the behavioral processes they encounter in everyday work.