Islington Country's First 20mph BoroughA 20mph speed limit is in place on all roads in Islington excepts main routes such as Pentonville Road.
The move has been made to make things safer for pedestrians, cyclists and road users and reduce noise and air pollution.
New signs have been put up over the last few months but there are no plans for extra traffic calming measures or speed bumbs.
Councillor Paul Smith, Islington Council's executive member for environment, said: "We're on the side of residents and this will make Islington's roads safer for everyone, whether they're walking, cycling or in a vehicle.
"It's a bold step, but there has been backing for a 20mph limit in Islington from residents, councillors and campaigners for safer streets.
"Islington is now the most complete 20mph borough in the country. We will closely monitor it to see how effectively it is working."
It comes as it is revealed that the number of people killed or seriously injured on Islington's roads fell from 227 in 2001 to 77 in 2009, partly as a result of lower speeds.