The men responsible for arranging the purchase of the Louisiana Territory were Robert Livingston and James Monroe.
Monroe and Livingston travelled to Paris in January 1803 to begin the negotiations of what would be the major territorial gain of the United States. At this time, the territory belonged to France after being a Spanish colony. President Thomas Jefferson put Monroe and Livingston in charge of the agreement, which would end in the purchase of the territory that nowadays conforms fifteen states.