The Biel–Täuffelen–Ins-Bahn near Bern, Switzerland was looking for a lighter train model to replace its aging fleet, so that a low floor system does not require heavy installations on the roof.
Based on that requirement Stadler came up with a concept of placing most of the equipment in a central unit between the seating cars.
While the BTI-Bahn tracks are meter gauge, Stadler presented the first prototype in 1995 set on standard gauge rails, and the Mittelthurgau-Bahn tested three prototypes on its standard gauge network during 1996.
The rolling stock for Mittelthurgau was later expanded to 10 GTW 2/6 (built 1998-1999) that are now part of the THURBO fleet (the three prototypes were sold to Italy).
The next lots were produced in meter gauge, and were delivered to the BTI-Bahn and the CEV-Bahn (Chemins de fer électriques Veveysans) in 1997 - although the BTI-Bahn was first to order any GTWs with its 7 trains, the CEV-Bahn ordered the biggest lot of the first generation with 20 trains.

In 1998 the Linzer Lokalbahn (Austria) placed an order which needed to be modified to conform to the DIN 5510 class 2 safety standard, as well as different electrification.
These 8 trains were delivered in 2000 from the Swiss facilities and an option of 6 more trains was fulfilled in 2005.
Another modification was done for the River Line (New Jersey) with an order of 20 DMUs delivered in 2002/2003 from the Swiss facilities.

During that time the Hessische Landesbahn (HLB) in Germany was also looking at the new system but actual procurement was delayed until the second generation.
In the beginning, Stadler was cooperating with ADtranz/DWA im Germany with the initial batch produced in 1999 at DWA Bautzen (Saxony).
Its headshape design follows the style of the Deutsche Bahn trains as they were already on production at DWA, and eventually the DB Regio services also ordered a batch of 30 trains of a similar type as the 30 trains ordered by the HLB (only the height of the low floor section differs).
The full series were then manufactured at the new Stadler Pankow (Berlin) facilities being built in 2000 by a joint venture with ADtranz.
Stadler acquired their shares in 2001 and the final vehicles were delivered from that plant in 2001 by Stadler alone.

The second generation can be easily distinguished by its round headshape made from FRP (glass-fiber reinforced plastic).
These follow the DB design being produced since 2000 for other customers as well, for example a batch of 12 trains went to Athens (Greece) in meter gauge (ordered in 1999, delivered since 2003).
With the second generation the available options for GTW trains expanded - meter gauge vehicles can be ordered in a 2.2 or 2.7m width and the standard gauge vehicles in a 3.0 or 3.1m width.
Also the GTW 2/6 may be expanded with an additional bogie car making it a GTW 2/8.

The third generation has minor modifications to the headshape but the more important changes were made to the power module - the electric variant now has 700-800 kW (instead of up to 520 kW) and the diesel-electric variant is available as a DMU-2 with two generators instead of one.
This allowed increasing the maximum speed, which was a requirement of Italian customers; in Italy this type is known as ATR 100.
 The Vinschgerbahn (Bolzano) was the first to order twelve DMU-2 in 2004, extended by eight vehicles of the same type for the Udine-Cividale line (Padova), also in 2004.
The DMU-2 concept impressed the Arriva operator in the Netherlands which ordered 43 trains in 2005 asking for some further developments - the modified type sold well to other operators in the Netherlands and abroad, both as DMU and EMU variants.

The fourth generation came along with new regulations in the EU that increased the crash worthiness requirements (see EN 15227).
 Trains had to comply with these requirements by 2008 (see 2008/57/EC).
This is the same year that much of the production was moved to the branch factory in Siedlce, Poland.

551 units have been sold until 2011 and are in use in Austria, France, Germany, Italy, the Netherlands, Slovakia,
The Biel–Täuffelen–Ins-Bahn near Bern, Switzerland was looking for a lighter train model to replace its aging fleet, so that a low floor system does not require heavy installations on the roof. Based on that requirement Stadler came up with a concept of placing most of the equipment in a central unit between the seating cars. While the BTI-Bahn tracks are meter gauge, Stadler presented the first prototype in 1995 set on standard gauge rails, and the Mittelthurgau-Bahn tested three prototypes on its standard gauge network during 1996. The rolling stock for Mittelthurgau was later expanded to 10 GTW 2/6 (built 1998-1999) that are now part of the THURBO fleet (the three prototypes were sold to Italy). The next lots were produced in meter gauge, and were delivered to the BTI-Bahn and the CEV-Bahn (Chemins de fer électriques Veveysans) in 1997 - although the BTI-Bahn was first to order any GTWs with its 7 trains, the CEV-Bahn ordered the biggest lot of the first generation with 20 trains.
In 1998 the Linzer Lokalbahn (Austria) placed an order which needed to be modified to conform to the DIN 5510 class 2 safety standard, as well as different electrification. These 8 trains were delivered in 2000 from the Swiss facilities and an option of 6 more trains was fulfilled in 2005. Another modification was done for the River Line (New Jersey) with an order of 20 DMUs delivered in 2002/2003 from the Swiss facilities.
During that time the Hessische Landesbahn (HLB) in Germany was also looking at the new system but actual procurement was delayed until the second generation. In the beginning, Stadler was cooperating with ADtranz/DWA im Germany with the initial batch produced in 1999 at DWA Bautzen (Saxony). Its headshape design follows the style of the Deutsche Bahn trains as they were already on production at DWA, and eventually the DB Regio services also ordered a batch of 30 trains of a similar type as the 30 trains ordered by the HLB (only the height of the low floor section differs). The full series were then manufactured at the new Stadler Pankow (Berlin) facilities being built in 2000 by a joint venture with ADtranz. Stadler acquired their shares in 2001 and the final vehicles were delivered from that plant in 2001 by Stadler alone.
The second generation can be easily distinguished by its round headshape made from FRP (glass-fiber reinforced plastic). These follow the DB design being produced since 2000 for other customers as well, for example a batch of 12 trains went to Athens (Greece) in meter gauge (ordered in 1999, delivered since 2003). With the second generation the available options for GTW trains expanded - meter gauge vehicles can be ordered in a 2.2 or 2.7m width and the standard gauge vehicles in a 3.0 or 3.1m width. Also the GTW 2/6 may be expanded with an additional bogie car making it a GTW 2/8.
The third generation has minor modifications to the headshape but the more important changes were made to the power module - the electric variant now has 700-800 kW (instead of up to 520 kW) and the diesel-electric variant is available as a DMU-2 with two generators instead of one. This allowed increasing the maximum speed, which was a requirement of Italian customers; in Italy this type is known as ATR 100.  The Vinschgerbahn (Bolzano) was the first to order twelve DMU-2 in 2004, extended by eight vehicles of the same type for the Udine-Cividale line (Padova), also in 2004. The DMU-2 concept impressed the Arriva operator in the Netherlands which ordered 43 trains in 2005 asking for some further developments - the modified type sold well to other operators in the Netherlands and abroad, both as DMU and EMU variants.
The fourth generation came along with new regulations in the EU that increased the crash worthiness requirements (see EN 15227).  Trains had to comply with these requirements by 2008 (see 2008/57/EC). This is the same year that much of the production was moved to the branch factory in Siedlce, Poland.
551 units have been sold until 2011 and are in use in Austria, France, Germany, Italy, the Netherlands, Slovakia,
Stadler GTW