This study explores the determinants of common ownership. Drawing on two explanatory lenses, we suggest an information-based perspective and a competition-based perspective. We theorize on and empirically test both perspectives at the firm, industry, and country levels. Based on 14,372 observations of firms from the MSCI All Country World Index for the years 2008 to 2017, we find evidence supporting the information-based perspective at the firm, industry, and country levels: Access to and the value of private information about rival firms increases common ownership. For the competition-based perspective, we find support at the industry and country levels, specifically uncovering that common ownership is higher in more concentrated industries and in countries with more extensive laws regarding anticompetitive conduct. Our findings contribute to research by stressing the relevance of both perspectives. Overall, our study has broader implications for understanding the emerging phenomenon of common ownership.