Restrictions on exports from the U.S. are to be taken seriously.  The existence of commercial opportunities for companies and individuals does not trump the interest of the U.S. government in restricting the sale, disclosure, financing, or export of certain products or information or the transacting of business with certain individuals or entities.  All transactions with foreign (and some domestic) parties, especially but not only those that are expected to lead to exports or imports, must be in compliance with applicable U.S. laws and regulations. 

CEOs, CFOs, salespeople, and others who paid no attention to the restrictions or who thought that their business really wouldn't be noticed or would escape through a technicality have experienced heavy fines, public embarrassment, and even imprisonment.  Although there are regulations under specific, narrower regimes, and a potential exporter should check with an export professional concerning regulations that might apply to specific products or services, the vast majority of restrictions fall within the following areas.  Even within these areas, the following is only a general description, and specific cases will require specific advice:

• Exports of "dual use" items, items that have a standard, obvious, publicly available purpose and a secondary purpose that could be turned against the United States or its citizens or military, OR a quite innocuous product or technology that is to be put to an inappropriate use.  An example is medical scanning software that can be easily adapted to different equipment, to allow artillery to shoot down incoming tactical missiles.  Another example is practically any item, such as consumer photography lenses, if their end use is to support a foreign military project or missile system.  Items on the Commerce Control List (CCL) of the Department of Commerce, and any item intended for potentially damaging use, is to be exported only under license.
• Exports of military items are controlled by the "ITAR" (International Traffic in Arms Regulation).  Most of these are items designed or modified specifically for the military.
• The OFAC (Office of Foreign Assets Control) of the U.S. State Department runs a program of sanctions against countries, regimes, and individuals.  See MGL Law Note 2.
• Several lists must be checked before a party covered by the regulations (U.S. citizens and permanent residents, as well as, usually, persons operating inside U.S. jurisdiction and, sometimes, subsidiaries or affiliates of U.S. companies) can proceed with a transaction or a relationship.  Doing business with a person or entity on one of the prohibited lists can lead to loss of the goods or funds involved, imposition of fines, and other penalties.  Check the following site for most of the relevant lists: http://export.gov/ecr/eg_main_023148.asp