Due to the amendment to the Polish Commercial Companies Code introduced by the Act of 19 July 2019, a new type of company will be introduced into the Polish legal system, with effect from 1 March 2021: namely, the simple joint-stock company. The simple joint-stock company is innovative through its free choice between a monistic and dualistic management system. This paper aims to consider selected aspects as regards the legal position and competences of the board of directors in the monistic system, including the new provisions covering i.a. the duty of loyalty, flexibility of the boards' structure and business judgment rule.