As a requirement of its mandate from the project sponsor, the MLA will be committed to raise the complete debt financing, which for a major project could be many hundreds of millions of dollars.
But, commercial lenders typically do not want to take more than a small part of the debt for a particular project and will want to pass some of the debt, and hence some of the risk, to other lenders.
The process of selling the debt is called syndication.
During the syndication process, one of the banks may fulfil the role of book runner.
The role of the book runner is simply to keep a record of how much debt each of the potential syndication banks wants to take.