The Boeing B-17 Flying Fortress is an American four-engined heavy bomber aircraft developed in the 1930s for the United States Army Air Corps (USAAC). A fast and high-flying bomber, the B-17 was used primarily in the European Theater of Operations and dropped more bombs than any other aircraft during World War II. It is the third-most produced bomber of all time, behind the American four-engined Consolidated B-24 Liberator and the German multirole, twin-engined Junkers Ju 88. The B-17 was also employed in transport, anti-submarine warfare, and search and rescue roles.

The following is an extensive catalogue of the variants and specific unique elements of each variant and/or design stage of the Boeing B-17 Flying Fortress, a heavy bomber used by the United States Army Air Forces and other Allied air forces during World War II.

United States Army Air Forces formations and units in the Mediterranean Theater of Operations (MTO) were the second-largest user of the Boeing B-17 Flying Fortress during World War II. There were a total of six combat groups (twenty-four squadrons) equipped with the bomber assigned to the Theater.