From the airport

Mumbai’s Chhatrapati Shivaji International Airport is about 28 kms from downtown Mumbai. The airport mainly consists of two terminals (Domestic and International) both using the same airspace and placed 4 kms apart. There is a free shuttle bus connecting them.
The safest and most convenient way to go from the airport to the city is by hiring a cab. Metered cabs are available outside the arrivals. Always ensure that the meter is turned down in front of you. A better option would be to take a taxi from the pre-paid service. You will get a coupon with the registration number of the taxi. Charges will depend on the general area of your destination and include all tolls etc. No subsequent payment has to be made.
Another option is to take a taxi/bus to Vile Parle station and then take a local train from there. This is more suitable in the evening as its off-peak direction then.

Most reputed hotels have their pick-up service at the airport and if you have already booked you should avail this service.