The William K. Bixby Papers includes a variety of materials, ranging from Bixby's personal correspondence relating to his collecting interests, through his connection with Washington University and the St. Louis Burns Club, and including many items from his manuscript collection.

The correspondence in each series is arranged chronologically. Items in other subseries are arranged alphabetically. The correspondence in Series I relates primarily to Bixby's collecting interests, publication of items in his manuscript collection, and his work on the Capitol Decoration Committee of Missouri, 1921-1927, 681 items. Series II contains items relating to gifts made by Bixby to Washington University, 1913-1927, 66 items. Series III contains items relating to the Burns Club of St. Louis but is in no way a complete archive of the Club's activities or of Bixby's relation to it, 80 items. Series IV contains autograph letters and related documents of notable individuals, primarily of significance in American and English literature and history, 891 items. Series V concerns Eugene Field and includes correspondence, numerous original manuscripts, editorial materials, printed items, and miscellaneous personal items, 281 items. A list of the correspondents included in each series precedes the section of the register devoted to that series. Included at the end of the register is a list of 15 items relating to John Paul Jones.