The league's official publication began as The Eastern Enigma. It originally contained few, if any, puzzles, and instead reported on business transacted at puzzlers' conventions, presented verses and skits composed by members, and relayed debates on the controversial puzzling topics of the day, such as obsolete words, esoteric references, and new types of puzzles.
Early editors rarely served more than a year at a time, and the publication schedule was often irregular. The January 1900 issue initiated a puzzle department called "Penetralia", which appeared regularly until 1903. "Penetralia" was resumed in the February 1910 issue, when The Eastern Enigma began monthly publication, and has continued to appear ever since. On the organization's name change, the magazine was retitled "The Enigma"; it continues to be published monthly and has now reached over 1200 issues.
A puzzle renaissance in the 1920s and 1930s led to a high point in NPL membership, during which it adopted the slogan "The National Intellectual Pastime of America". The biennial conventions were covered by major newspapers and wire services. During World War II, the Signal Intelligence Service recruited several NPL members as government cryptographers based on their puzzling experience.
In the 1960s, membership slumped significantly, but began rebounding in the "modern" puzzling era with the promotional efforts of Dmitri Borgmann, Ross Eckler, and others. Many of the leading puzzle editors and constructors in America are members; author and member Willard Espy said of the league's expertise, "I'm a little nervous talking about wordplay with this group .... it's like talking about religion with God."
NPL members are known collectively as "the Krewe" and individually as "Krewepersons", "Krewemembers", or "NPLers".
Puzzle professional Will Shortz is a long-standing member and officer of the NPL, currently serving as its historian (since 1992).
The NPL has also published several editions of Guide to The Enigma (formerly Key to Puzzledom); a mini-sample of the puzzles in The Enigma, available free to prospective members from the editor; a member directory; and book compilations of hard cryptograms and cryptic crosswords.
The NPL concentrates puzzles into four primary categories. The oldest two are the "flat" (which has a one-line answer) and the "form" (which has a multi-line answer). Flats (verse puzzles and anagrams) were a leading type of wordplay before black-squared crosswords were invented. They look strange to modern puzzlers, because they require inferring words from context, which is not now a familiar solving technique. Nonetheless, flats today still make up most of the puzzles in The Enigma. Cryptograms and extras, as well as catchall categories for rule-breaking puzzles, were added later. More information on these puzzle types can be found at the NPL's official website.