Most agents can be divided into two broad groups: those who represent clients on a case-by-case basis and those who have intensive, ongoing partnerships with clients. Literary agents typically do not have long-term relationships with clients except for established authors. They may work with writers just one time, electing to represent them only after reading manuscripts and determining their viability. Literary agents market their clients' manuscripts to editors, publishers, and television and movie producers, among other buyers. Many of the most prestigious magazines and newspapers will not consider material unless an agent submits it. Busy editors rely on agents to screen manuscripts so that only the best, most professional product reaches them. Sometimes editors go directly to agents with editorial assignments, knowing that the agents will be able to find the best writer for the job.