The Bureau of Industry and Security (BIS) is responsible for implementing and enforcing the Export Administration Regulations (EAR), which regulate the export and reexport of most commercial items. We often refer to the items that BIS regulates as "dual-use" - items that have both commercial and military or proliferation applications - but purely commercial items without an obvious military use are also subject to the EAR.
For more information please visit the Bureau of Industry and Security webpage:
http://www.bis.doc.gov/licensing/exportingbasics.htm
Exports concerning military items are under the jurisdiction of the U.S. Department of State.