I think it's executive agreements. They are arranged by the President while treaties must have the approval of two-thirds of the Senate.
http://www.law.asu.edu/library/RossBlakleyLawLibrary/ResearchNow/ResearchGuides/TreatiesandInternationalAgreements.aspx
Most agreements with foreign nations are in the form of:
A. executive agreements.
B. treaties.
C. statutory arrangements.
D. ex parte proceedings.
This one is really confusing. I am torn between A & B. My textbook says both and looking on line says both as well.
3 answers
Note that this site says that since 1939, about 90% of the relations with foreign nations have been handled with executive agreements.
http://constitution.findlaw.com/article2/annotation12.html
http://constitution.findlaw.com/article2/annotation12.html
For instance, trade, inspection, military agreements on bases, ships, etc, airline landing rights, are all exectutive agreements.