The airport is roughly 30km from central Beijing.
Taxi - taxi ranks are found outside all 3 terminal buildings (Terminal 1, 1st floor, outside Gate 1; Terminal 2 1st floor, outside Gates 5-9; Terminal 3, outside exit, level B1). Only use metered taxis from the official waiting line. Licensed taxis in Beijing all have a plate that starts with “京 B” and offer printed receipts - most have a yellow stripe along the middle of the car. If you don't speak Mandarin, consider getting the name of your destination written in Simplified Chinese or have a map handy - if you are unable to do this prior to arrival, the information or hotel desks may be able to help you.
Bus - city buses and long-distance services are available to and from the airport. There are ticket offices on the first floor of all 3 terminals.
Train - the Airport Express line of the Beijing Subway (also known as ABC) has stations at Terminals 2 and 3, and provides services roughly every 10 minutes to Sanyuanqiao and Dongzhimen Metro stations. Trains run 7 days a week from 6 a.m. to 11 p.m. and are the fastest route into the city. Note that the journey times are different depending on the direction of travel - this is because the trains reverse at Terminal 3 and wait at Terminal 2. Although it's a subway line, the journey to and from the airport is on an elevated line above ground. Taking substantial luggage on subway connections from the Airport Express line is not recommended as trains can be standing room only.
Hotel shuttle - free shuttle buses run from the airport to nearby hotels including the Hilton Beijing Capital Airport Hotel, the Ibis Beijing Capital Airport Hotel and the Langham Place. There are around 30 hotels in the vicinity of the airport ranging from budget to 5-star.
Car rental - you'll find car rental desks in Arrivals at Terminals 2 and 3. At Terminal 1, cars can be hired from the hotel information desk between Gates 1 & 3 on the first floor.