This book provides solid sociological foundations to computational social science (CSS). CSS is an emerging research field, and many books with those words in the title are on the market. However, CSS has not become mainstream in sociology, for which there are two reasons. First, CSS does not necessarily solve major research questions in sociology. Second, its sociological foundations are weak. These two reasons are interrelated—that is, CSS cannot solve major research questions because its sociological foundations are weak. Thus, even if it tries to solve those questions, its approaches seem to mainstream sociologists to miss the point. To resolve that shortcoming, this book fills the gap between CSS and sociology, shows that CSS can solve major research questions in sociology, and advances sociology by introducing to it theories and methodologies of CSS.