The paper describes the main characteristics of ownership structure of Turkish nonfinancial firms listed on the Istanbul Stock Exchange (ISE) and examines the impact of ownership structure on performance and risk-taking behavior of Turkish firms. Turkish corporations can be characterized as highly concentrated, family owned firms attached to a group of companies generally owned by the same family or a group of families. Ownership structure is defined along two attributes: concentration and identity of the owner(s). We conclude that there is a significant impact of ownership structure—ownership concentration and ownership mix—on both performance and risk-taking behavior of the firms in our sample. Higher concentration leads to better market performance but lower accounting performance. Family owned firms, in contrast to conglomerate affiliates, seem to have lower performance with lower risk. Government-owned firms have lower accounting but higher market performance with higher risk.