As the title implies, the job of a music historian is to research and study people, places, events, artifacts, written and recorded materials pertaining to music history. They present their findings through writing books, creating audio-visual presentations, giving specches and interviews. Also see Music History 101
A person who has backgrounds in both library science and music. Aside from working in libraries, they can also work with orchestras, television and radio stations, publishing companies and others. Music librarians catalog and maintain music collections, help organize events and assist researchers, among others. More information from the Music Library Association
The role of the music publisher is to assist and protect the rights of composers and songwriters. They make sure the songwriter or composer is properly compensated for their work and that contracts are honored, They also help songwriters and composers promote their compositions. Other obligations are stated in a publishing contract between the songwriter/composer and the music publisher. A publisher gets a percentage from royalties incurred by the copyrighted music. More information from the Music Publishers Association.
Orchestrating means to write or compose music for an orchestra. An orchestrator knows how to combine several instruments in order to come up with a beautiful composition that tells a story. Also see What is an Orchestra?