Taxis are plentiful and relatively cheap. Drivers use meters but can take out-of-towners for a ride, literally, by not taking the most direct route. If you book a cab from a hotel or restaurant, have someone speak to the driver so there are no "misunderstandings" about your destination. The meter starts at EUR 1.95 during the day and EUR 2.30 at night and during weekends. You pay what is on the meter. Supplementary charges are added for luggage (EUR 1.50) and if you phone for a cab (EUR 0.75). The meter generally isn't used for journeys outside Lisbon, so you'll have to agree on a fare.
You may hail cruising vehicles, but it's sometimes difficult to get drivers' attention; there are taxi stands at most main squares. Remember that when the green light is on, it means the cab is already occupied. Tips—10% or so—for reliable drivers are appreciated.
Autocoope (21/793-2756). Rádio Táxis (21/811-9000). Télétaxi (21/811-1100).