For such an iconic American subject, the literature of the Lewis and Clark expedition is surprisingly sparse, probably because the journals themselves, until the Moulton edition made them widely available, were so difficult to find in a complete authoritative form. We do not have too many books about Lewis and Clark; we have too few. Here are the 10 best.
Gary E. Moulton, ed., The Definitive Journals of Lewis and Clark (Lincoln: University of Nebraska Press, 1983-2001).
If you want Lewis and Clark whole, this is the edition to buy. Moulton spent more than two decades pulling the pieces together and did a masterly job. If you don’t want the atlas volume or the herbarium or the index volume, which are available only in hardcover, volumes 2-8, which contain the journals of Lewis and Clark, can be had in paperback. So can volumes 9-11, which contain the journals of Patrick Gass, Joseph Whitehouse, John Ordway, and Charles Floyd.