The English language has been shaped by a number of other languages over the centuries, and many English speakers know that Latin and German were two of the most important. What many people don't realize is how much the French language has influenced English.
Without going into too much detail, I want to give a little bit of background about the other languages which shaped English. It was born out of the dialects of three German tribes (Angles, Jutes, and Saxons) who settled in Britain in about 450 A.D. This group of dialects forms what linguists refer to as Anglo-Saxon, and at some point this language developed into what we know as Old English. This Germanic base was influenced in varying degrees by Celtic, Latin, and Scandinavian (Old Norse) - the languages spoken by invading armies.
Bill Bryson calls the Norman conquest of 1066 the "final cataclysm [which] awaited the English language." (1) When William the Conqueror became king of England, French took over as the language of the court, administration, and culture - and stayed there for 300 years. Meanwhile, English was "demoted" to everyday, unprestigious uses. These two languages existed side by side in England with no noticeable difficulties; in fact, since English was essentially ignored by grammarians during this time, it took advantage of its lowly status to become a grammatically simpler language and, after only 70 or 80 years existing side-by-side with French, Old English segued into Middle English.
During the Norman occupation, about 10,000 French words were adopted into English, some three-fourths of which are still in use today. This French vocabulary is found in every domain, from government and law to art and literature - learn some. More than a third of all English words are derived directly or indirectly from French, and it's estimated that English speakers who have never studied French already know 15,000 French words. (2) You can see 1,700 words that are identical in the two languages right here: True cognates.
English pronunciation owes a lot to French as well. Whereas Old English had the unvoiced fricative sounds [f], [s], [θ] (as in thin), and [∫] (shin), French influence helped to distinguish their voiced counterparts [v], [z], [ð] (the), and [ʒ] (mirage), and also contributed the diphthong [ɔy] (boy). (3) (What is voiced/unvoiced/fricative?)
Another rare but interesting remnant of French influence is in the word order of expressions like secretary general and surgeon general, where English has retained the noun + adjective word order typical in French, rather than the usual adjective + noun used in English.
If you are interested in French and/or English linguistics and would like to learn more about their reciprocal relationship, please visit the links and the further reading resources below.
Page 2: French Vocabulary in English
Sources and Further Reading
(1) The Mother Tongue: English & How It Got That Way, by Bill Bryson (compare prices)
(2) French is Not a "Foreign" Language!, American Association of Teachers of French.
(3) The American Heritage Dictionary of the English Language, ed. Houghton Mifflin Company (compare prices)
French Inside Out: The French Language Past and Present, by Henriette Walter (compare prices)
Honni soit qui mal y pense : L'incroyable histoire d'amour entre le français et l'anglais, by Henriette Walter (vendor's site)
The Languages of the World, by Kenneth Katzner (compare prices)
Made in America: An Informal History of the English Language in the United States, by Bill Bryson (compare prices)