English is a Germanic language that originated from dialects brought to Britain by Germanic invaders. Most of this migration occurred during the 5th century from various parts of what is now northwest Germany, Denmark and the Netherlands. It was a time during which Germanic peoples were migrating en masse under pressure from population growth and invading Asian groups. They traveled in far and diverse directions going as far south as the Mediterranean and northern Africa.

One of these incoming Germanic tribes was the Angles and the names 'England' and English are derived from the name of this tribe. However Saxons, Jutes and a range of Germanic peoples also moved to Britain in this era. The Germanic dialects combined to form what is now called Old English. The invaders' Germanic language displaced the indigenous languages in most of what is now England. The original Celtic languages remained in parts of Scotland, Wales and Cornwall.

Old English did not sound or look like the Standard English of today. Any native English speaker of today would find Old English unintelligible without studying it as a separate language. Nevertheless, about half of the most commonly used words in Modern English have Old English roots. The words be, strong and water, for example, derive from Old English. The most famous surviving work from the Old English period is the epic poem Beowulf which was composed by an unknown poet.

Before arriving in Britain, the Angles, Saxon and Jutes had traded and fought with the Roman Empire. As a result many Latin words, some of which had Greek origins, entered into their vocabulary and were a part of old English from the beginning. Examples of such words include butter, devil, dish, kitchen, pillow, street and wall. The introduction of Christianity in the 6th century and 7th century added another wave of Latin and Greek words.

Later, English was strongly influenced by the Northern Germanic language Old Norse. Norseman - "people from the North" - were primarily from southern and central Scandinavia and settled in the north-east of England in the 8th and 9th centuries. The new and the earlier settlers spoke languages from different branches of the Germanic family. While the roots of much of their vocabulary and expressions were the same, their grammars were more distinct. Contact with Old Norse might have lead to the simplification of Old English, including the loss of grammatical gender and case. English words of Old Norse origin include anger, bag, both, hit, law, leg, same, skill, sky, and take. The pronoun 'they' might even be of Norse origin.

The Norman conquest of England began on the 28th of September 1066 with the invasion of England by William, Duke of Normandy. Later he became known as William the Conqueror after his victory at the Battle of Hastings on the 14th of October 1066 when he defeated king Harold II of England. By early 1071, William had secured control of most of England, although rebellions and resistance continued for another twenty years.

The Norman conquest was a pivotal event in English history. It largely removed the native ruling class, replacing it with a foreign, Norman speaking monarchy, aristocracy, and clergy. Norman was a Gallo-Romance language related to the Parisian French dialect which became modern French. From 1066 until Henry IV of England ascended to the throne in 1399, the royal court of England spoke a Norman language. English continued to be the language of the common people. No attempt was made by the rulers to suppress it. In 1204 the Normans lost their territories in Normandy, becoming wholly English. By the time Middle English arose as the dominant language in the late 14th century, the Normans had contributed roughly 10,000 words to English. 75% of these words remain in use today.

There is a tendency for Norman-derived words to have more formal connotations. Most modern English speakers would consider a "cordial reception" (from Norman) to be more formal than a "hearty welcome" (Germanic). Another example of the influence of Norman is the words of animals being separate from the words for their meat. For example beef and pork (from the Norman bœuf and porc) are the products of 'cows' and 'pigs', while the animals themselves retained their Germanic names.

In the 15th century English underwent a pronunciation change. Known as the Great Vowel Shift, it marks the beginning of Modern English. The works of William Shakespeare and the King James Bible are Modern English. When the United Kingdom became a colonial power, English became the language of the colonies of the British Empire.

Due to its assimilation of many European languages, modern English contains a very large vocabulary. The Oxford English Dictionary lists over 250,000 distinct words excluding many technical and slang terms. Approximately 375 million people speak English as their first language. English today is the third largest language by number of native speakers, after Mandarin Chinese and Spanish. However, when combining native and non-native speakers it is the most spoken language in the world. Because English is so widely spoken, it has often been referred to as a "world language". While it is not an official language in most countries, it is currently the language most often taught as a foreign language. It is no longer the exclusive cultural property of "native English speakers", but is a language that is absorbing aspects of cultures worldwide as it continues to grow. English itself is now open to language shift as multiple regional varieties feed back into the language as a whole. The 'English language is forever evolving'.