Language. Tamil is the state language and Tamil identity around language is strong. English is widely understood in hotels, restaurants and by younger people, and is common in business. Hindi is much less useful here than in northern India — don't assume it will be understood, and it is better received to try English or a few words of Tamil. "Vanakkam" (hello) and "nandri" (thank you) go a long way.
Dress. Chennai is more conservative than Mumbai or Bengaluru. Modest clothing is appreciated generally and expected at religious sites.
Alcohol. Sold only through state-run TASMAC outlets and licensed bars and hotels. Legal drinking age is 21. Dry days apply on certain national holidays.
Beach safety. Do not swim at Marina Beach. Currents and undertow are dangerous and there are regular drownings. Elliot's Beach is somewhat safer but still requires caution. Beaches south along the ECR are generally better for swimming.
Heat management. If visiting between March and June, plan sightseeing for before 10am and after 5pm. Drink far more water than feels necessary. Heat exhaustion is a genuine risk.
Monsoon awareness. During October to December, check weather forecasts daily. Flooding can close roads with little warning and disrupt airport and rail services. Build flexibility into travel plans.
Water. Drink only sealed bottled or properly filtered water. Avoid ice in informal establishments. Street food is generally excellent but choose busy stalls with high turnover.
Transport. Use app cabs rather than negotiating with auto-rickshaws unless you're comfortable bargaining. Traffic is heavy; allow far more time than distance suggests, especially crossing the city at peak hours.
Temples. Remove footwear before entering (there are usually minded shoe stands for a small fee). Some temples restrict non-Hindus from inner areas. Photography is often prohibited inside — look for signs. Avoid visiting during personal menstruation if you wish to respect local custom, as some temples request this.
Money. ATMs are widespread. UPI digital payments are near-universal, including at small shops, though this generally requires an Indian bank account. Cards are accepted at established businesses; carry some cash for autos, small eateries and markets.
Bargaining. Expected in markets and with auto-rickshaws, not in showrooms, malls or restaurants.
Timing your visit around Pongal. Mid-January is festive but many businesses close for several days and transport is heavily booked. Plan accordingly.
Connectivity. Mobile data is cheap and coverage is excellent. Buy a local SIM (Airtel, Jio, Vi) on arrival — you'll need passport and visa copies plus a photo.