Introduction

In the last few years, the board composition of listed companies has been strongly affected by new laws and social equality pressure from media, stakeholders, and investors. From a political perspective, the most important innovation is the gender quota, which has been introduced in eight countries starting with Norway in 2003. This quota has strongly changed the board composition in countries that have adopted it. This binding quota is intended to promote gender diversity to improve social equality and increase firm performance; however, the last relation, which has been studied in depth in the last few years and in different countries, has not highlighted a clear relationship. We must also consider that differences in terms of age and nationality are also an important source of heterogeneity. The last two elements have been studied thoroughly by researchers around the world, and in this case, the results are strongly in contrast. Researchers have also analyzed a different type of heterogeneity called “occupational heterogeneity.” This heterogeneity seems to be one of the most important sources of competitive advantage generated by a board of directors.