Familiness, perceived as family members' involvement in and influence on the functioning of the family business, constitutes the distinguishing feature of every family firm. In the paper, we empirically test the relationships between familiness, innovation input and output and organizational performance in a post‐transition economy using data from 200 Polish family firms. Our research results reveal that high levels of ownership, management and control of the firm by the family members, perceived as part of familiness, lead to increased firm performance. Second, results show that the increase in the degree of familiness lowers the innovation input. We also found out that increases in the transgenerational orientation of a family business and family–employee bonds lead to decreased innovation output and higher family business identity generate higher innovation output.