The InterRegio is a train service seen in some European countries. Mostly they are trains that run "from region to region", as best described by Swiss Federal Railways.
In Belgium, InterRegio (IR) trains were slower than the fast IC trains, and usually called at more stations along a route. Their journey was usually not as long as IC trains, but still traveled further than the local (L) trains.
Most IR trains had hourly frequencies, some having only services every two hours (although this is mostly true only for weekend services).
All trains in Belgium shared the same cost structure, so taking an IR train costed the same as an IC or L train for the same route. The only difference lay in the number of station stops they call at.
In December 2014 the InterRegio was withdrawn, InterRegio lines were either converted to InterCity or Local train or cancelled completely.
The InterRegio in Switzerland was first introduced in 1997. They replaced some of the former fast trains with their own identity (InterRegio).
InterRegio trains are now very commonplace in Switzerland. The abbreviation is IR in a 45°-edgy font, white letters on red.
The ICN runs as an InterCity train but sometimes with halt frequencies in the same manner as an IR (Geneva/Lausanne-St. Gallen/Basel route) and sometimes as IC trains (Basel-Chiasso). When ICN services first began on May 28, 2000, the ICN was placed as an InterRegio train.
InterRegio trains were also commonplace in Germany from 1988 to 2003. They travelled and mainly connected regions in Germany. Most of the InterRegio lines have been replaced by InterCity lines; a few were replaced by the newly established Interregio-Express (IRE) type. However, Interregio-Express lines belong technically to the short distance train category, and tend to be shorter. InterRegio trains were very popular as they could be used without supplement - DB scrapped them, hoping customers would trade up to InterCity (IC) or InterCity Express (ICE) trains, a policy that was only partially successful, and then only when the SparPreis brand of tickets were introduced.