Aspen Insurance Holdings Limited is a Bermuda-based holding company. The Company provides insurance and reinsurance coverage to clients in various domestic and global markets through wholly owned operating subsidiaries in Bermuda, the United States and the United Kingdom, as well as its branch operations in Canada, Singapore and Switzerland. It manages its underwriting operations as two business segments: Insurance and Reinsurance. The Insurance segment underwrites primarily specialty risks across a diversified set of property and casualty lines of business. The Insurance segment is organized into four primary portfolios of business: financial and professional lines; casualty and liability lines; first party lines, and specialty lines. The Reinsurance segment is organized into four portfolios: casualty reinsurance, property catastrophe reinsurance, other property reinsurance and specialty reinsurance. Its casualty reinsurance is written on an excess of loss and proportional basis.