It all started with a dream.
Stephenie's dream that she had
on June 2, 2003. 
"I know the exact date that I began writing Twilight, because it was
also the first day of swim lessons for my kids. So I can say with
certainty that it all started on June 2, 2003. Up to this point, I had
not written anything besides a few chapters (of other stories) that I
never got very far on, and nothing at all since the birth of my first
son, six years earlier.
I woke up (on that June 2nd) from a very
vivid dream. In my dream, two people were having an intense conversation
in a meadow in the woods. One of these people was just your average
girl. The other person was fantastically beautiful, sparkly, and a
vampire. They were discussing the difficulties inherent in the facts
that A) they were falling in love with each other while B) the vampire
was particularly attracted to the scent of her blood, and was having a
difficult time restraining himself from killing her immediately. For
what is essentially a transcript of my dream, please see Chapter 13
(“Confessions”) of the book."
-Stephenie Meyer
I couldn't let this day go by without celebrating
and acknowledging it. :)