This study addresses the relationship between founder ownership and firm value in young and entrepreneurial businesses. We argue that a stewardship effect prevails when founders have low or high levels of ownership whilst an agency effect prevails at intermediate levels. Using a dataset of 1,269 firms with 11,645 firm–year observations, we find support for our hypothesis that there is a convex relationship between founder ownership and firm value. The agency effect at intermediate founder ownership is consistent with evidence indicating that these firms display lower leverage, greater unrelated diversification, and higher disproportionate board representation.