WSIA’s membership consists of approximately 400 brokerage member firms, 100 company member firms and 200 associate member firms, all of whom operate over 1,500 offices representing approximately 15,000 to 20,000 individual brokers, insurance company professionals, underwriters and other insurance professionals serving the U.S. surplus lines insurance market from around the globe. WSIA is unique in that both surplus lines brokers and surplus lines insurance companies are voting members of the Association; thus WSIA represents and speaks for the surplus lines wholesale marketplace.

Incorporated in 1975 as wholesale broker organization, WSIA (formerly NAPSLO) now is comprised of four membership classifications: Wholesale Brokers, Companies, Underwriting Managers, and Associates.