What are the primary differences between a short story and a novel?

The primary difference between these two genres is length
and depth of focus.  A novel is organized by chapters, and will typically begin with
some sort of expository information about one more more characters.  Novels will often
have sub-plots accompanying the main plot, because there is more time to develop these;
character development for a novel tends to be more in-depth as well.  It is easier to
develop a complex, multi-faceted character in a novel because of the extended length. 
Short stories sometimes skip the exposition all together, and head straight into the
rising action.  Like many movies, novels will also sometimes have an anti-climax, or
place where you think the story has reached its maximum emotional impact, only to be
followed later by the true climax of the story.