At the start of World War II, the German Army was divided into 17 military districts (Wehrkreis), which were each assigned Roman numerals. The camps were numbered according to the military district. A letter behind the Roman number marked individual Stalags in a military district.
Sub-camps had a suffix "/Z" (for Zweiglager - sub-camp). The main camp had a suffix of "/H" (for Hauptlager - main camp).
Some of these sub-camps were not the traditional POW camps with barbed wire fences and guard towers, but merely accommodation centers.
The camps for Allied airmen were run by the Luftwaffe independently of the Army.
The camp for Allied seamen was run by the Kriegsmarine independently of the Army.