This collection consists of letters, dating from 1787 to 1844, from John Lewis Guillemard, an English aristocrat, traveler, and science enthusiast, to his family and friends, specifically, his sister, Jeanne Marie Griffin, his nieces Frances, Jane and Mary Griffin, his uncles, James and Isaac Guillemard, Sir John and Lady Jane Griffin Franklin, and Sir George Thomas Staunton.

In his letters from America, Guillemard documents among other things, the country's political situation, foreign relations with France and Great Britain following the Revolutionary War, as well as his service as a commissioner to the Jay Treaty. Frequent trips to the Continent, particularly France, Italy, and Switzerland, result in Guillemard's witnessing of significant political and social upheavals, including the French Revolution, specifically the aftermath of the capture of the Bastille, and to a lesser extent, the Neapolitan War of 1815. Guillemard's letters also document the early 19th-century scientific and intellectual communities and their advancements, the British Empire, as well as family and financial affairs.

Much of the collection's description is based on dealer information and research.