If you want to know who agented a particular book, there are a variety of ways how to discover the individual literary rep who made the deal. Here are three ideas for starters:
1. Simply check the book's acknowledgements. Sometimes, it will be as simple as a writer saying, "And a special thanks to my agent, Randy Masterson."
2. Use search engines. Try Googling the book's title (or author) and the word "agent," and see what you come up with.
Also, lots of times, authors will have their representation listed online. So if you want to know who the agent was for Joe Smith's book, The Neptune Paradox, find Joe Smith's official Web site. Check the bottom of the home page, and then the "Contact" page. The site may say, "Joe is represented by Randy Masterson Literary Agency, 245 Manhattan Road, New York, NY."
3. Worse case scenario, you can call the publisher. If you see that Knopf published the book, for example, call Knopf's main line and speak to the operator. Ask for the editorial department; better yet, if you can, explain your goal and request to speak with the editor who worked on The Neptune Paradox. The operator will say, "Oh, that's Judy Smith. I'll transfer you." You won't talk to Judy, but rather her assistant. No matter. Ask the assistant if Judy did indeed edit The Neptune Paradox. When the assistant confirms Judy's involvement, kindly request to know who the book's acting literary agent was. She'll be happy to tell you.