This study analyzes the relationship between implementing a Family Constitution (Protocol) and future family business performance. We analyze a unique sample of 530 Spanish family businesses. Half of these firms received financial aid from the government to implement a Family Protocol during 2003-2013. The analysis reveals that family businesses that implemented a Family Constitution had significantly improved performance within 2 years after the implementation. The positive relationship between the implementation of a Family Constitution and future firm performance is stronger for firms that had a nonfamily CEO, had multiple family owners, or were controlled by later generations.