In 2006, sleek extra-long buses replaced the city's many competing private services when the bus and metro were united as Transantiago, a government-run public transportation system that's quick, cheap and efficient for getting around central Santiago. The Transantiago website has downloadable route maps and a point-to-point journey planner.
You'll need a tarjeta Bip! (a contact-free card you wave over sensors). You pay a nonrefundable CH$2700 for a card, and then 'charge' it with as much money as you want. Two people can share a card, and they also work on the metro. Transantiago charges CH$720 during rush hour (7am to 9am and 6pm to 8pm) and CH$640 the rest of the time. One fare allows you two hours in the system, including multiple transfers.