I totally agree with pukesick. This is one of the most amazing books I have read.
The story is of Fredric Henry, an American in the Italian army, who drives ambulances, and Catherine Barkely, an English nurse.
The story is not really being told by Fred Henry, but it is more like he is writing it down. There are two Freds in the story, the one writing it and the one in it. This is very apparent in lines such as "I wish she was here now" and "as I can not tell it now."

I won't go into the whole story, but the main underlying theme is that death is inevitable, and Fred Henry has accepted this, especially in the context of war. The most amazing quote in the book relates to this:
    "If people bring so much courage to this world the world has to kill them to break them, so of course it kills them. The world breaks every one and afterward many are strong at the broken places. But those that will not break it kills. It kills the very good and the very gentle and the very brave impartially. If you are none of these you can be sure it will kill you too but there will be no special hurry."