Literary agents
It is the literary agent's job to find publishers for the writers they represent. They negotiate contracts on the writer's behalf and can also manage and plan a writer's career.
In return for working for a writer the agent receives a percentage (usually around 10%) of the writer's income from advances, fees and royalties.
Before a literary agent agrees to represent a writer they will want to read the writer's manuscript. So be sure to contact an agent only when you have something concrete to offer. However, like publishers, literary agents prefer not to be sent unsolicited manuscripts. It will save you time and reduce your chances of rejection if you research the agents most suitable to approach. Find out whether they represent writers who write the kind of book you've written. Some deal exclusively with writers of screenplays; others are only interested in writers of children's books.