Books of travels, journals, and voyages have become so numerous, and are so frequently impositions on the public, that the writer of the following sheets feels under an obligation to explain, in some measure, the original circumstances that led to the production of this volume. Soon after the purchase of Louisiana by an enlightened administration, measures were taken to explore the then unknown wilds of our western country--measures founded on principles of scientific pursuits, combined with a view of entering into a chain of philanthropic arrangements for ameliorating the condition of the Indians who inhabit those vast plains and deserts. His Excellency, Meriwether Lewis, then a captain of the first regiment of infantry, was selected by the President of the United States, in conjunction with Captain C. Clarke [Wm. Clark], to explore the then unknown sources of the Missouri, and I was chosen to trace the Mississippi to its source, with the objects in view contemplated by my instructions; to which I conceived my duty as a soldier should induce me to add an investigation into the views of the British traders in that quarter as to trade, and an inquiry into the limits of the territories of the United States and Great Britain. As a man of humanity and feeling, I made use of the name of my government to stop the savage warfare which had for ages been carried on by two of the most powerful nations of aborigines in North America. Why I did not execute the power vested in me by the laws of the country, to ruin the British traders and enrich myself, by seizing on the immense property of the North West Company, which I found in the acknowledged boundary of the United States, will be explained by my letter to Hugh M'Gillis, Esq., to whom I own eternal gratitude for his polite and hospitable treatment of myself and party. In the execution of this voyage I had no gentleman to aid me, and I literally performed the duties (as far as my limited abilities permitted) of astronomer, surveyor, commanding officer, clerk, spy, guide, and hunter; frequently preceding the party for miles in order to reconnoiter, and returning in the evening, hungry and fatigued, to sit down in the open air, by firelight, to copy the notes and plot the courses of the day.