Buses are reliable, cheap and comfortable. Some companies offer very large, cosy airplane-style reclining seats. Reservations are advisable on weekends and holidays. Buses are severely air-conditioned so pack a blanket or warm clothes. The easiest way to buy a ticket is either from the bus station itself or from a convenience store, such as 7-Eleven.
For routes and companies see Taiwan Bus (www.taiwanbus.tw/). Two of the biggest companies are Kuo Kuang and UBus.
There's an extensive network from Taipei to Kenting National Park and across the north as far as Yilan. Service from the west coast to the east coast is limited to a few buses a day from Taichung across to Hualien and Kaohsiung to Taitung. Service is also limited within the east area (from Hualien to Taitung).
On the west coast there are very frequent departures (some 24-hour operations), with midweek and late-evening discounts. Most companies serve the same west-coast routes. The main transit points are Taipei, Taichung, Tainan and Kaohsiung.
The network is wide, but there are few daily departures except to major tourist destinations (such as Sun Moon Lake). In most cases you are better off taking the tourist shuttle buses.
Taiwan has an excellent system of small shuttle buses with well-planned routes that connect major and minor tourist sites and destinations. The buses usually leave hourly on weekdays and half-hourly on weekends.
Single fares or one-day unlimited tickets are available. Children under 12, seniors and student card holders travel for half price.
See www.taiwantrip.com.tw for information on timetables, fares and routes in English.
Fares vary by city. For example, a single zone fare in Taipei is NT$15, while in Kaohsiung it's NT$12. The cost of travelling in two zones is double the price of a one-zone fare.
Sometimes you pay when you get on and sometimes when you get off. If you cross a zone, you pay when you get on and again later when you get off. As a general rule, follow the passengers ahead of you or look for the characters 上 or 下 on the screen to the left of the driver. The character 上 (up) means pay when you get on; 下 (down) means pay when you get off. If you make a mistake the driver will let you know (or likely just shrug it off).