The collection consists of envelopes both used and unused (also known as covers), letters, postcards, documents, postage stamps, and a variety of other philatelic material from around the world as collected and annotated by William Hogarth Tower (Princeton Class of 1894). Rev. Tower's collection spans the topics of English Postal History, United States Postal History, War Covers, Philatelic Miscellany, and Franking. A baked clay tablet letter enclosed in a partially broken case (circa 2200 B.C.), from Drehem, Mesopotamia, is the earliest item in the collection.

The next earliest letters in the collection date from the late fourteenth through the fifteenth centuries in Europe. There are signed letters or documents by royals such as King Charles II, King George II, Queen Caroline, and King William IV, as well as a small pencil sketch of his own royal frank by King Edward VIII. English postal history is well illustrated by letters from or to nobleman such as Edward Harley, Hugh Percy, Thomas Fairfax and his son, Ferdinando Fairfax. Letters from notable persons during the Colonial American period include: Joseph Dudley, George Washington, Benjamin Franklin, Isaiah Thomas, and a love letter from William Bradford to his future wife, Susan Boudinot.

Two volumes in the collection are devoted to the topic of Abraham Lincoln in philately. Another volume focuses on Arctic philately and contains single letters from John Franklin, C. F. Hall, Princeton University's Edward Libbey, Fridtjof Nansen, Roald Amundsen, and Richard Evelyn Byrd. The majority of this volume contains material from A W. Greely's 1881 Arctic Expedition that was later recovered in 1899 from Fort Conger during Robert Peary's expedition.

Tower's War Cover volumes contain examples from the U.S. Civil War, World War I, and World War II, as well as many other conflicts around the globe throughout the centuries. Single letters of interest include a military dispatch to Emperor Napoleon from one of his generals and a letter by the Duchess of Richmond about her husband and sons at the Battle of Waterloo.

It should be noted, however, that most of the covers and letters collected by Tower are from 'ordinary' people and were considered significant, not for the contents inside, but for the postal marks on the outside of the envelope or the locations from which they were mailed.