When you're a writer, whether you've been published or not...it makes no difference...and you don't have a literary agent representing you, you are your own agent. You are representing yourself, on your own behalf, always looking out for your own best interests. This is important to understand, especially with so many changes happening in publishing.
This is the wiki definition of a literary agent, here. It's easier to just link than explain, because that's not the reason for this post.
For a few brief months in my 20 year writing career, I had a literary agent. It didn't work out. We parted amicably when I wound up sending her checks at the end of each quarter. I was basically shopping and selling my own work faster than she could get out an e-mail reply. My books were being released faster than she (bless her dear little slow beating heart) could tweet them. And other than that experience, I've always acted as my own agent. I've made mistakes along the way. I've also been lucky enough to have good friends in publishing who can, and have, advised me when I didn't understand something. But for the most part, I've been winging it on my own. And I've learned how to think before I act in every single situation I encounter.
The reason I'm writing this post isn't about me. It's not about literary agents either. I'm writing it because I've heard more than one author in the past six months make statements I'm not sure they understand. Several have said they are releasing their books through Amazon as Kindle e-books. Almost all of them used wording like, "Amazon is acting as my agent."
I'm all for what Amazon is doing for authors. Amazon is empowering them and giving them chances the so-called "gatekeepers" would never have done. And almost every author I know is now taking advantage of this opportunity, as they should. But Amazon is not acting as an author agent. Amazon is looking out for their own best interests, and that's what the author should be doing, too.
There are many books and web sites out there that discuss self-publishing or Indie Publishing, whichever you prefer. There are also books and web sites that help unagented authors. I've learned a lot just by reading literary agent blogs in the past ten years. But it's important to understand that if you don't have a professional literary agent looking out for you, you'd better be looking out for yourself. And you'd better start learning how to do that. It's just as important with Indie Publishing, digital release first publishing, and e-publishing in general as it's always been with "traditional" publishing.