This study examines the relationship between multinationality and the performance of Japanese manufacturing companies during the period 1999-2008 by using geographic segment information. Despite the enormous interest in and importance given to multinationality from the academic and business worlds, prior findings about the multinationality-performance relationship are conflicting and inconsistent. The overall results of the present study show that multinationality has a positive impact both on accounting performance and on market-based performance. In additional tests, Japanese electric and electronic equipment companies’ reliance on the Asian market was found to have a negative impact on profitability and no significant impact on firm value, whereas reliance on other foreign markets such as the Americas and the EU had a positive impact on profitability and firm value. The multinationality-performance relationship cannot be generalized and varies among geographic regions. This book contributes to both the multinationality-performance literature and the geographic segment reporting literature by offering empirical evidence about Japanese manufacturing companies and comparing them with prior findings about American companies.