This study assesses the interactive effects of product diversification (PD), multinationality (MN), and country involvement (CI) on firm performance, and explores these effects not only in pairs but also in groups. It locates the optimal combinations of these three variables that will help firms to maximize their performance. The results indicate that when these three variables interact in pairs (that is, MN and CI, respectively, interact with PD), their impact on firm performance are opposite, when they interact as a group (MN and CI jointly interact with PD), they mutually strengthen or cancel each other out, and the optimal combinations differ depending on the interactions of PD with MN and CI. [ABSTRACT FROM AUTHOR]