There is no train into Houston, and we recommend taking the bus over a taxi as they run frequently and are a lot more affordable.
Bus
METRO Bus 102 takes you straight to downtown Houston in around one hour. The bus terminates at the Downtown Transit Center at Gray and La Branch. Buses run from 05:04-00:34 every 15 minutes at peak times and every 30 minutes at off-peak times. Find information and schedules here.
Location: South side of Terminal C, arrivals, baggage claim level
Cost: USD 1.25
Buying tickets: On the bus in cash (only with exact change)
Taxi
All destinations from the airport are charged according to the flat zone rate or the meter rate, whichever is less. The journey time is about 20 minutes. A surcharge of USD 2.75 applies for a departure fee, and an additional surcharge of USD 1.00 applies for late-night trips between 20:00-06:00.
Location:
South side of Terminal A, before security, arrivals, Door A-115
South side of Terminal B, before security, arrivals, Door B-103
South side of Terminal C, before security, arrivals, Door C-106
West side of Terminal E, before security, arrivals, Door E-102
Cost: USD 53 to downtown Houston, USD 60 to Galleria/Medical Center area, USD 105 to NASA Space Center
Rideshare
To cut transportation costs, you may want to use rideshare options such as Uber, Lyft, Wingz or Get Me. Ridesharing options at the airport are marked as "Transportation Network Company".
Location:
South side of Terminal A, before security, arrivals, Door A-115
South side of Terminal B, before security, arrivals, Door B-103
South side of Terminal C, before security, arrivals, Door C-106
West side of Terminal E, before security, arrivals, Door E-102
Airport shuttle
An airport shuttle can save you money and these are available from a variety of companies. For example, Express Shuttle USA (713) 523-8888 takes you to downtown Houston for USD 23.