Cockney speakers have a distinctive accent and dialect, and frequently use Cockney rhyming slang. There are also several borrowings from Yiddish, including kosher (originally Hebrew, via Yiddish, meaning legitimate) and stumm (pronounced shtoom with a short oo sound, meaning quiet). A fake Cockney accent, as used by some actors, is sometimes called 'Mockney'.

The lengthening of the vowel sound was a Cockney innovation which spread and by 1900 was used by many southern English accents. Most of the features mentioned above have in recent years partly spread into more general south-eastern speech, giving the accent called Estuary English); an Estuary speaker will use some but not all of the Cockney sounds. The characteristics of Cockney as opposed to Estuary are the dropping of H and grammatical features like the use of ain't.

It's also worth noting that as Chatham Dockyard expanded during the 18th Century, large numbers of workers were relocated from the dockland areas of London, bringing with them a "Cockney" accent and vocabulary. Within a short period this famously distinguished Chatham from the neighbouring areas, including the City of Rochester, which had the traditional Kentish accent.

A television advert for Heineken beer in the 1980s showed a Sloane woman receiving elocution lessons in Cockney, parodying My Fair Lady. In the advert, she was being taught to say "The wa'er in Majorca don' taste like wo' i' ough' a", but could only manage a posh rendition of "The water in Mallorca doesn't taste quite how it should" (until, of course, she drank the beer).