Mario Andrew Pei (1901-1978) was an Italian-American linguist and polyglot, who wrote a number of popular books known for their accessibility to readers without a professional background in linguistics.
Pei was born in Rome, Italy, and immigrated to the United States with his parents in 1908. By the time he was out of high school he knew not only English and his native Italian but also Latin, Greek, and French. Over the years he became fluent in several other languages (including Spanish, Portuguese, Russian, and German) capable of speaking some 30 others, and acquainted with the structure of at least 100 of the world's languages.
In 1923, he began his career teaching languages at City College in New York, and in 1928 he published his translation of Vittoria Ermete de Fiori's Mussolini: The Man of Destiny. Pei received his doctorate from Columbia University in 1937, focusing on Sanskrit, Old Church Slavonic, and Old French
In 1937, he joined the Department of Romance Languages at Columbia University, becoming a full professor in 1952. In 1941, he published his first language book, The Italian Language. His facility with languages was in demand in World War II, and Pei served as a language consultant and served with two agencies of the Department of War. As a consultant, he wrote language textbooks, developed language courses and wrote language guidebooks.
While working as a professor of Romance Philology at Columbia University, Pei wrote over 50 books, including the best-sellers The Story of Language (1949) and The Story of English (1952). His other books included Languages for War and Peace (1943), A Dictionary of Linguistics (written with Frank Gaynor, 1954), All about language (1954), Invitation to linguistics: a basic introduction to the science of language (1965), and Weasel Words: Saying What You Don't Mean (1978).
Pei also penned The America We Lost: The Concerns of a Conservative (1968), a book advocating individualism, constitutional literalism, and other paleoconservative principles. In the book, Pei denounces the income tax, as well as communism and other forms of collectivism.
Mario Pei was also an internationalist who advocated the introduction of Esperanto into school curricula across the world to supplement local languages.
On the value of neologisms
In noting that neologisms are of immense value to the continued existence of a living language, and that most words are developed as neologism from root words, Pei stated in The Story of Language:
"Of all the words that exist in any language only a bare minority are pure, unadulterated, original roots. The majority are "coined" words, forms that have been in one way or another created, augmented, cut down, combined, and recombined to convey new needed meanings, The language mint is more than a mint; it is a great manufacturing center, where all sorts of productive activities go on unceasingly." 
On creative innovation and slang
"While slang may be condemned by purists and schoolteachers, it should be remembered that it is a monument to the language's force of growth by creative innovation, a living example of the democratic, normally anonymous process of language change, and the chief means whereby all the languages spoken today have evolved from earlier tongues."
"Far from rejecting Esperanto...I have been advocating it for a long time." (Personal letter to this contributor, 1969)
- French Precursors of the Chanson de Roland, 1949, AMS Press, ISBN B000NYKM5G
- Story of Language, 1949, Lippincott, ISBN 0397004001
- All About Language, 1950, Lippincott, ISBN B000NL744Q
- Liberal arts dictionary in English, French, German [and] Spanish, 1952, Philosophical Library, ISBN B0006AT8DO
- Liberal Arts Dictionary (with Frank Gaynor), 1952, Philosophical Library, ISBN B000I8VRIS
- A Dictionary Of Linguistics (with Frank Gaynor), 1954, Philosophical Library, ISBN B0006ATY1U
- Language For Everybody;: What It Is And How To Master It, 1956, New American Library, ISBN B0007DP9OM
- Getting Along in Italian, 1958, Bantan, ISBN B000DCOI9E
- One Language for the World, 1958, Biblio-Moser, ISBN 0819602183
- Getting Along in Russian, 1959, Harper, ISBN B0007DXBC4
- Getting Along in French (with John Fisher), 1961, Bantam, ISBN B000NUTKXK
- 109 Most Useful Foreign Phrases for the Traveler, 1962, Curtis, ISBN B000MV0GA6
- Voices of Man: The Meaning and Function of Language, 1962, Harper & Row, ISBN B000JHJQ54
- The Story of English: A Modern Approach, 1962, Premier, ISBN B000GSCNHE
- Invitation to Linguistics: A Basic Introduction to the Science of Language, 1965, Doubleday, ISBN 0385065841
- Getting Along in German (with Robert Politzer), 1965, Bantam, ISBN B000ERICZE
- Glossary of Linguistic Terminology, 1966, Columbia University Press, ISBN 0231030126
- Studies In Romance Philology And Literature, 1966, Garnett Publishing, ISBN B000N7BCY8
- Words in Sheeps Clothing, 1969, ISBN B000LQ5FAS
- Talking Your Way Around the World, 1971, Harper-Collins, ISBN 0060133279
- Getting along in Spanish, 1972, Bantam, ISBN B0007HEDP4
- Weasel Words, 1972, Harper & Row, ISBN B000NUH8ES
- How To Learn Languages And What Languages To Learn, 1973, Harper & Row, ISBN 0060133236
- Families of Words, 1974, St Martins Press, 0312280351
- Dictionary Of Foreign Terms, 1975, Delacorte Press, ISBN 0440017793
- What's In A Word? Language: yesterday, today, and tomorrow, 1975, Universal, ISBN B0007EJK0K
- The Story of Latin and the Romance Languages, 1976, Harper-Collins, ISBN 0977326403
- New Italian Self-Taught, 1982, Harpercollins, ISBN 006463616X
- Swords for Charlemagne: (Swords of Anjou), 1955, Graphic Books, ISBN B0007HBNRA
- THE CONSUMER'S MANIFESTO: A Bill Of Rights to Protect the Consumer in the Wars Between Capital and Labor, 1960, Crown Publishers, ISBN B000J0KWB8
- Our National Heritage, 1965, Houghton Mifflin, ISBN B0007DP9WE
- America We Lost: The Concerns of a Conservative, 1968, World Publishing, ISBN B000OKGUTQ
- Tales of the natural and supernatural,, 1971, Devin-Adair, ISBN B0006C5INQ
Remarks on the Esperanto Symposium
Mario Pei On Esperanto Education
One Language For The World