From Academic Kids
The nuclear envelope refers to the double membrane of the nucleus that encloses genetic material in eukaryotic cells. It separates the contents of the nucleus (DNA in particular) from the cytosol. The space between the two membranes that make up the nuclear envelope is called the perinuclear space, and is usually about 20 - 100 nm wide. The outer membrane is continuous with the rough endoplasmic reticulum.
The nuclear envelope may also play a role in the disposition of chromatin inside the nucleus.