In pursuance of a measure submitted to Congress by a message of January 18th, 1803, and sanctioned by their appropriation for carrying it into execution, Captain Meriwether Lewis, of the first regiment of infantry, was appointed, with a party of men, to explore the river Missouri from its mouth to its source; and, crossing the highlands by the shortest portage, to seek the best water communication thence to the Pacific ocean; and Lieutenant Clarke was appointed second in command. They were to enter into conference with the Indian nation on their route, with a view to the establishment of commerce with them. They entered the Missouri, May 14th, 1804, and on the 1st of November, took up their winter quarters near the Maudan towns, 1609 miles above the mouth of the river, in latitude 47° 21´ 47´´ north, and longitude 99° 24´ 45´´ west, from Greenwich. On the 8th of April, 1805, they proceeded up the river in pursuance of the objects prescribed to them. A letter of the preceding day, April the 7th, from Captain Lewis, is herewith communicated. During his stay among the Maudans', he had been able to lay down the Missouri according to courses and distances taken under his passage up it, corrected by frequent observations of longitude and latitude, and to add to the actual survey of this portion of the river, a general map of the country between the Mississippi and Pacific, from the thirty-fourth to the fifty-fourth degrees of latitude. These additions are from information collected from Indians with whom he had opportunity of communicating during his journey and residence among them. Copies of this map are now presented to both houses of Congress. With these I communicate, also, a statistical view, procured and forwarded by him, of the Indian nations inhabiting the territory of Louisiana, and the countries adjacent to its northern and western borders; of their commerce, and of other interesting circumstances respecting them. In order to render the statement as complete as may be, of the Indians inhabiting the country west of the Mississippi, I add Dr. Sibley's account of those residing in and adjacent to the territory of Orleans. I communicate also, from the same person, an account of the Red river, according to the best information he had been able to collect.