The chapter investigates, through a systematic literature review, the current state of knowledge on the relationship between diversity (in terms of age, culture, physical abilities and disabilities, ethnicity, gender, etc.) and firm performance (broadly understood as economic, environmental, social, innovative, etc.). The systematic literature review is conducted by using the MySLR platform which allows for the identification of two main research topics. Topic one is focused on “Gender diversity and performances” while topic two is focused on “Other diversities (ethnic, cultural, age, disabilities) and performances.” After the description of the two topics, an interpretation of the results within the input–mediator–outcome framework is proposed. The results of the analysis are useful to provide some thoughts in order to identify gaps in the literature and, consequently, academic implications for future research directions. Particularly, the relationship between diversity and performance has not been given serious attention in the context of public administrations; this context is also worthy of further study. Furthermore, greater attention in research should be deserved to disability and to understanding how disability management and inclusion systems in the firms can impact different performances. Finally, the relationship between migrant employees and firm-level performance deserves further study and research.