Arch Capital is a Bermuda-based specialty insurer and reinsurer that writes insurance, reinsurance, and mortgage insurance worldwide. The insurance segment covers specialty P&C lines including casualty, construction, E&S, professional lines, and middle market commercial, with the 2024 acquisition of Allianz's U.S. Middle Market P&C and Entertainment businesses expanding Arch's presence in that space. The reinsurance segment covers property, casualty, specialty, and property catastrophe lines on both proportional and excess-of-loss bases. The mortgage segment writes U.S. primary mortgage insurance (required on low-down-payment loans sold to the GSEs), lenders' mortgage insurance in Australia, and mortgage insurance and credit risk transfer transactions in Europe. Arch makes money through underwriting profit and investment income on its $47.4B investment portfolio. Underwriting discipline is central to the model — Arch emphasizes risk selection and pricing over volume growth, actively allocating capital toward lines with the best risk-adjusted returns and pulling back where margins are insufficient. Arch also holds minority stakes in several insurance-related entities, including Somers Re, Premia, and Coface. When organic deployment opportunities are limited, Arch returns capital to shareholders through buybacks; Arch repurchased ~$1.9B of shares in 2025.