In recent years, firms' innovation activities have been encouraged in many countries, and the topic of innovation performance has been of interest to researchers. Previous studies have confirmed that internal sources have an impact on innovation performance, while external sources have gained increasing popularity and influence on firms' activities. Despite the growing interest in the impact of external sources on innovation performance, most studies have reached conflicting conclusions, with some showing positive effects and others negative effects. Therefore, the question remains as to whether external sources can affect innovation performance. This study aims to clarify the role of external sources on innovation performance by reviewing, analyzing, and synthesizing results from 56 empirical studies conducted worldwide. The findings highlight the theoretical frameworks used in previous studies and the types of external sources, such as external knowledge, R&D, information technology, and spillovers from foreign enterprises, that affect innovation performance. Finally, the study proposes suggestions for future research.