Static models of interacting persons measured at the interval level are reviewed. A discussion of the fundamental sources of variance and key design decisions in social-interaction research is presented. Outlined are the basic designs for social-interaction research and their proper analysis. Multilevel modeling is likely to become the most common data analysis method. Critical issues unique to social-interaction research are examined, particularly the effect of the partner on the interaction actor. Finally, illustrations of analyses from four extended examples are presented.