A literary agent is someone who sells rights (usually book publication rights - but increasingly, other rights too - such as film rights, television rights, electronic rights) in work created by writers. Not all writers need a literary agent. However, many major publishers and virtually all film studios or production companies prefer that submissions (manuscripts or screenplays sent to them for consideration) should come via an agent. Having a good agent will increase - but not guarantee - your chances of getting published. A good agent will also negotiate a satisfactory contract on your behalf, ensure that you're paid on time, and do a hundred and one other things that writers need doing.