Tze-Chiang (Chinese: 自強號; pinyin: Zìqiáng háo), also Tzu-chiang or Ziqiang, is a type of limited express train service operated by Taiwan Railway (TR). Of the five service classes operated by TR, the Tze-Chiang service is the fastest. Ticketing is done on the basis of mileage (NT$2.27 per km with a 10 km minimum fee).

This service is operated with 6 different trainsets: the E1000 series, EMU3000, TEMU1000 (Taroko Express), DR2800, DR3100, and the TEMU2000 (Puyuma Express). The now-retired EMU100 was the first trainset built for this service, which was used for 30 years, terminating ordinary runs at on 15 June 2009.

Taiwan Railways' West Coast Mainline (WCML) Electrification Project was completed in 1978, leading wholesale timetable recast on the WCML. At about the same time, the new EMU100 vehicles ordered for express passenger service on the WCML was introduced. Up until this point, the highest-class passenger train on the WCML had been the diesel and electric locomotive hauled Kwan-Kung (Tourist) Express, which was phased out of service on 25 April 1978. All express passenger schedules were re-allocated to a new class of deluxe electric express service, and the Chu-Kuang Express (introduced earlier in 1970).

Tze-chiang was so-named from a phrase in an address that Chiang Kai-shek, the former President of Republic of China (Taiwan), delivered to his countrymen on 26 October 1971 in response to United Nations Resolution 2758, in which he urged the country to "Respect the Homeland, Strengthen Self ("Tzu-chiang"); Respond to Change without Fear." U.N. Resolution 2758 formally recognised Beijing as the government of "China" and de-recognized Taipei, at the same time revoking Taipei's U.N. membership. For this reason, the Tzu-chiang is also sometimes referred to as the "Self-Strengthening Express".^{[citation needed]}

The EMU100 "electric express" was formally introduced on 15 August 1978 at a fare of NT$1.32 per kilometer. The first services operated between Taipei and Taichung (via Coast Line), and as electric catenaries were erected, switched to operating via Mountain Line. As the service was extended to Chiayi and Tainan, the service was formally christened "Tze-Chiang Limited Express". As electrification progressed, the service was eventually extended to between Keelung and Kaohsiung.

After 1980, other equipment was introduced and assigned to Tze-Chiang service, including EMU200, EMU300, E1000 Push-Pull, TEMU1000 tilting train on electrified lines, and DR2800, DR2900, and DR3000 on non-electrified lines. From 6 July 1991 through 31 March 1992, the Taiwan Railways Administration (TRA) piloted business class service on selected departures. However, due to low ticket sales, the experiment was terminated. In 2010, TRA redesignated certain former business class coaches (BCK) on the Chu-Kuang Express as Tzu-chiang.

As of 2013, the next generation of tilting trains, designated the TEMU2000 series, has been introduced into commercial service. They are intended to replace the DR2800, DR2900, and DR3000 series of DMUs as the Eastern Line's electrification completes.

In the early 1970s, the West Coast Mainline Electrification Scheme was already planned. Taiwan Railways had ordered 94 electric locomotives, and also 13 five-car electric multiple unit sets from General Electric Company. Identified as the EMU100 series, the set included driving power coach 50EP100, motor coach 55EM100, two trailers 40ET100, and driving trailer 40ED100. The sets were assembled by British Rail Engineering Limited's York Carriage Works in 1976. Throughout 1978 the sets were delivered to Taiwan for testing and acceptance.