The top 100 international (re)insurance groups account for 85% of the global insurance assets and thus are the driving force of global insurance supply. Yet little is known about their internal structure, business focus and the international footprint. We fill the gap by providing the first comprehensive analysis of the structure and complexity of the global insurance groups. We construct and analyze a novel dataset on the corporate structure of the top 100 global insurance groups with headquarters located in 21 countries and their 8,000 subsidiaries located in 117 countries and offshore territories. We document how the level of internationalization and the business focus of foreign subsidiaries vary across headquarters regions as well as developed and emerging markets. Then we examine the measures of business and geographic complexity of groups and relate them to insurers’ performance characteristics, global risk sharing and systemic risk.