No excerpt-field in post edit

Hi!

Looked around for an hour or so now, but cant find anything usefull. I used to be alone on my blog, and only use the defult account. Now we are a bunch of ppl, each with our own account. But when any one of us are going to create a new post, the Excerpt-field below the post-field in the editor is gone. Can some one tell me how to activate this again? It only shows up on the first account created.

Thanks in advance guys!