The underwriter (investment bank) that is in charge of, and has ultimate control on, an initial public offering (IPO). The bookrunning job is considered the most important in any IPO, as a bookrunner is responsible for maintaining the list of orders placed by institutional investors in the IPO (i.e., the book of demand) and then determining the proper allocations of stock to such investors. Practically, there can be more than one underwriter appointed as a bookrunner (in which case the group of underwriters are called co-bookrunners). A bookrunner can also be a deal sponsor, global coordinator and lead manager. However, not all of them can be appointed as a bookrunner.

The bookrunner is also referred to as the lead underwriter or bookrunning manager.