Book Description: This book examined human interactions in relation to adjustments to groups. Especially, these studies focused on self-assertion as a factor produced the difference in human interactions. As a consequence, following results were obtained. People who asserted themselves clearly were satisfied with their human interactions. In addition, people, who were satisfied with their human interactions, were also satisfied with their groups. Moreover, they tried to achieve their tasks diligently. Therefore, I have suggested the importance of self-assertion with respect to the adjustment to groups. Author Biography: Hitoshi Yoshimura is an assistant professor of psychology at Kochi Gakuen College, Japan. His primary research interests include peer interaction, interpersonal behavior and leadership. His studies have focused on adolescence or early childhood. Recently, in addition, he published a book on childcare. He has also been concerned with adjustment to groups for returnee students or foreigners living in Japan.