Residents of Chennai are called Chennaiites. As of 2001, Chennai city had a population of 4.2 million, while the total metropolitan population was 6.4 million. The estimated metropolitan population in 2006 is 7.0 million.

Ranganathan Street in T.Nagar is usually packed with pedestrian shoppers.

The population density in the city is 24,418 per km² while the overall population density is 5,847 per km². The sex ratio is 948 females for every 1000 males, slightly higher than the national average of 934.The average literacy rate is 80.14%, much higher than the national average of 59.5%. 18% percent of the city's population is classified as living in slum conditions.

The main problem Chennai faces is overpopulation and resulting water scarcity. Residential skyscrapers are generally not favoured, leading to urban sprawl, with consequent increase in commuting time and ownership of private vehicles. High land prices and the lack of space has pushed many members of the lower strata of society into residing in slums, which tend to have poor sanitation and lack of access to clean water.

The majority of residents in Chennai are Tamilians and speak Tamil. English is widely spoken, especially in business, education and other white collar professions. Tamil spoken in Chennai uses English words liberally, so much so that it is often called Madras bhashai (Tamil for "Madras language"). There are also sizeable Malayalee, Telugu and Urdu speaking communities. A regional hub since British times, other prominent communities include Marwari, Anglo Indian, Bengali, Punjabi, Gujarati communities and people from Uttar Pradesh and Bihar. Chennai also has a growing expatriate population who work in the industries and IT centres.