The Rosette Nebula is an emission nebula, a large star forming region in the constellation Monoceros, the Unicorn.
It is a large cloud of gas and dust that lies near a large molecular cloud and is closely associated with the open cluster NGC 2244, whose stars were formed from the nebula's matter in the last five million years.

Technical info: 
TS 80mm f6 APO triplet refractor - (modified) Canon 40D - exposure 18min (9x120sec)