English is a multi-center language. Due to the wide use of English, various regional varieties inevitably appear. Linguists no longer regard upper-class English in London or Britain as the only standard English. Besides British English, the most important ones are North American English and Australian New Zealand English.

Since 17 and 18 centuries, American English, Canadian English, Australian English and New Zealand English have become unique dialects. They also have their own regional vocabulary, grammar and pronunciation. Other languages, such as Indian English, Southeast Asian English, Caribbean English and some emerging countries in Africa, are all influenced by local languages and have phonetic and lexical characteristics.

The main dialects of English have obvious differences in pronunciation, but there are little differences in spelling. Generally speaking, people use dictionaries of some academic institutions as standard English, such as Oxford English Dictionary. In academic and scientific articles, authors from all over the world use the same style.

Before World War II, the term "American English" was usually understood as a unique American word and grammar. In the eyes of some "purist" British scholars at that time, it was not pure English, but before and after World War II, the concept of "American English" gradually changed, referring only to English used in the United States, regardless of its similarities and differences with British English.

After World War II, due to the rapid development of American mass media, American English in turn had an impact on other dialects, and this impact was expanding day by day.