This thesis responded to three main objectives, developed in the form of three interconnected articles, which used the roles played by the Boards of Directors (CAs) of companies in the basic segment of Corporate Governance of B3 Brasil Bolsa Balcão S.A as an explanatory variable. The determination of the roles was inferred by a content analysis of 2,394 decisions contained in the Minutes of Meetings of the Board of Directors (CA), in the period 2014–2018, based on the classification proposed by Schwartz-Ziv and Weisbach (2013). The first objective observed that the roles, managerial and supervisory, predominantly exercised by the CA affected the rate of corporate investment in fixed assets, identifying that these roles were significantly and distinctly related to that rate; the managerial one affected it positively, and the supervisory one, negatively, suggesting that the managerial performance of the CA stimulates investment due to the focus on Management, while the supervisory one inhibits it. In this sense, the work deepened the analysis to identify whether the increase or decrease in the level of investment was accompanied by an improvement in investment efficiency (EI). Thus, the second objective investigated whether the predominance of each role was related to IE, since its improvement is obtained by reducing information asymmetry and agency conflicts — a role assigned to the Board of Directors by the Agency Theory (AT). The results report that management boards are associated with a decrease in inefficiency related to underinvestment, while in supervisory boards, the opposite occurs. Also, it was observed that neither of the two roles was significantly associated with the reduction of global inefficiency and overinvestment, suggesting that, in the companies in the sample, the form of action of the Board of Directors was indifferent to explain the overinvestment, so it was not possible to argue that the two roles would be associated with the increase or decrease of excess investment motivated by agency conflicts (empire building, excess confidence, etc.). In turn, the third objective analyzed the permanent investment in participations in other companies, since greater disbursements in this type of investment would increase the number of subsidiaries and affiliated companies of the business group, increasing agency problems and the difficulty of monitoring due to the high number of transactions between the companies of the group, demanding more from the Board. Based on this, we tested the hypothesis that the predominance of the supervisory role is associated with the decrease in the number of companies in the group due to the focus on monitoring. The data reported that the holdings in the sample, with a predominantly managerial role of the CA, had, statistically, a median of controlling/affiliated companies higher and different than those whose role was supervisory, however, the predominance of this role was not significantly associated, to the reduction in the number of subsidiaries. The document analysis also indicated that the managerial role occurred more frequently, and most of the decisions made were about “financial” and “formal” issues or related to the area of “personnel and benefits”. None of the papers were related to a greater participation of institutional investors in the Board room.