A secondary underwriter that is involved, along with other underwriters, in an initial public offering (IPO). An issuer may hire more than one underwriter when it decides to go public. Underwriters are selected through a process known as a bake-off. A company may select more than one underwriter for reasons related to showing more credibility. One a company selects an underwriter or co-underwriters, it calls for an all-hands meeting.

A co-underwriter is also known as a co-manager.