One aspect of American and British English pronunciation differences is differences in accent. The General American (GAm) and the Southern British Received Pronunciation (RP) accents have some significant points of difference, described in this article. However, other regional accents in each country may show greater still differences, for which see regional accents of English speakers.
Phonological differences

* GAm is rhotic while RP is non-rhotic; that is, the phoneme /r/, or what was historically a phoneme /r/, is only pronounced in RP when it is immediately followed by a vowel sound. Where GAm pronounces /r/ before a consonant and at the end of an utterance, RP either has nothing (if the preceding vowel is /ɔː/ or /ɑː/, as in bore and bar) or has a schwa instead (the resulting sequences are diphthongs or triphthongs). Similarly, where GAm has r-coloured vowels (/ɚ/ or /ɝ/, as in cupboard or bird), RP has plain vowels /ə/ or /ɜː/. However many British accents, especially in Scotland and the West Country, are rhotic, and there are a few non-rhotic accents in the United States, especially in urban working-class areas like New York, Boston, and a few conservative dialects of Southern American English (especially among older-speakers). Non-rhoticity is also very common among speakers of African-American Vernacular English, which is a dialect that influences a great portion of African-American speakers to varying degrees.
* The "intrusive R" of many RP speakers (in such sequences as "the idea-r-of it") is absent in GAm; this is a consequence of the rhotic/non-rhotic distinction.
* For some RP speakers (upper class), unlike in GAm, some or all of tire, tower, and tar are homophones; this reflects the merger of the relevant vowels; similarly the pour-poor merger is common in RP but not in GAm.
* RP has three open back vowels, where GAm has only two or even one. Most GAm speakers use the same vowel for RP "short O" /ɒ/ as for RP "broad A" /ɑː/ (the father-bother merger); many also use the same vowel for these as for RP /ɔː/ (the cot-caught merger).
* For Americans without the cot-caught merger, the lot-cloth split results in /ɔː/ in some words which now have /ɒ/ in RP; as reflected in the eye dialect spelling "dawg" for dog.
* The trap-bath split has resulted in RP having "broad A" /ɑː/ where GAm has "short A" /æ/, in most words where A is followed by either /n/ followed by another consonant, or /v/, /ð/, /z/, /s/, /f/, or /θ/ (e.g. plant, pass, laugh, path).
* RP has a marked degree of contrast of length between "short" and "long" vowels (The long vowels being the diphthongs, and /iː/, /uː/, /ɜː/, /ɔː/, /ɑː/). In GAm this contrast is much less evident, and the IPA length symbol (ː) is often omitted.
* The "long O" vowel (as in boat) is realised differently: GAm pure [oː] or diphthongized [oʊ]; RP central first element [əʊ]. However there is considerable variation in this vowel on both sides of the Atlantic.
* The distinction between unstressed /ɪ/ and /ə/ (e.g. roses vs Rosa's) is sometimes lost in GAm. In RP it is retained, in part because[citation needed] it helps avoid non-rhotic homophones; e.g. batted vs battered as /ˈbætɪd/ vs /ˈbætəd/. It is, however, lost in Australian English (which is also non-rhotic) meaning both words are pronounced the same, unlike American or British English.
* Where GAm has /iː/ in an unstressed syllable at the end of a morpheme, conservative RP has /ɪ/, not having undergone happY tensing. This distinction is retained in inflected forms (e.g. candied and candid are homophones in RP, but not in GAm).
* In GAm, flapping is common: when either a /t/ or a /d/ occurs between a sonorant phoneme and an unstressed vowel phoneme, it is realized as an alveolar-flap allophone [ɾ]. This sounds like a /d/ to RP speakers, although many GAm speakers distinguish the two phonemes by aspirating /t/ in this environment, especially after /ɪ/ or /eɪ/ (thus bitter and rated are distinguishable from bidder and raided), or by lengthening the vowel preceding an underlying /d/. [ɾ] is an allophone of /r/ in conservative RP, which is hence caricatured in America as a "veddy British" accent. The degree of flapping varies considerably among speakers, and is often reduced in more formal settings. It does occur to an extent in nearly every speakers of American English, with "better" pronounced with a flap almost ubiquitously regardless of background. Pronouncing the t would be considered overly-formal. This does not mean it always completely merges with "bedder", as many speakers enunciate the d as to distinguish it slightly from the flapped t.
* Yod-dropping occurs in GAm after all alveolar consonants, including /t/, /d/, /θ/, /s/, /z/, /n/, /l/; i.e. historic /juː/ (from spellings u, ue, eu, ew), is pronounced /uː/ in a stressed syllable. In contrast, RP speakers:
o always retain /j/ after /n/: e.g. new is RP /njuː/, GAm /nuː/;
o retain or coalesce it after /t/, /d/: e.g. due is RP /djuː/ or /dʒuː/, GAm /duː/;
o retain or drop it after /θ/, /l/: e.g. allude is RP /əˈljuːd/ or (as GAm) /əˈluːd/.
o retain, coalesce or drop it after /s/, /z/: e.g. assume is RP /əˈsjuːm/ or /əˈʃuːm/, or (as GAm) /əˈsuːm/;
+ In some words where /j/ has been coalesced in GAm, it may be retained in RP: e.g. issue is RP /ˈɪsjuː/ or (as GAm) /ˈɪʃuː/