In today’s market, probably 80 percent of books published by New York houses get sold by literary agents. Agents are experts in the publishing industry and represent the interests of their author-clients. They have inside contacts with specific publishers and know which editors are most likely to buy a particular work. Perhaps most important, agents can secure the best possible book deal for you, negotiate a fair contract, protect your rights, ensure you are paid accurately and fairly, and run interference when necessary between you and the publisher.
The best agents are career-long advisers and managers.