WordStream is backed by Sigma Partners , a leading early-stage venture capital firm founded in 1984. The Sigma team uses their deep operational experience to provide entrepreneurs with practical strategic counsel through every phase of company growth. With over $2 billion under management and east and west coast offices, Sigma invests in innovative technology startups across the United States. The team is currently investing Sigma Fund 8, a $500 million fund raised in 2007. Some of the market leading companies in which Sigma has invested include Atria, Cascade, Clarify, EqualLogic, Internet SecuritySystems, KLA-Tencor, m-Qube, Octel, Topio, VeriFone, Vermeer, Vignette and Virtusa.
In May 2010 WordStream secured additional Series B funding from Egan-Managed Capital . Egan-Managed Capital was founded in 1997 with an eye toward helping finance and support early-stage New England technology companies offering enterprise-class products and services. Egan-Managed Capital’s current and past portfolio includes high-tech companies such as Apparent Networks, HighStreet Networks, IntelliVid, Network Intelligence, Novera, and uTest.
After demonstrating strong business and revenue growth, WordStream secured $12 million of venture capital funding led by Baird Capital  of Chicago, Illinois. Baird, the private investment arm of Robert W. Baird & Co., specializes in investments in companies operating within the technology & services and healthcare sectors. Baird has invested in more than 45 companies, including Amphora Medical, GenomeDX Biosciences, NimbleGen Systems and Zurex Pharma.