A railgrinder (or rail grinder) is a maintenance of way vehicle or train used to restore the profile and remove irregularities from worn tracks to extend its life and to improve the ride of trains using the track. Rail grinders were developed to increase the lifespan of the tracks being serviced for rail corrugation. Rail grinding is a process that is done to stop the deformation due to use and friction on railroad tracks by removing deformations and corrosion. Railroad tracks that experience continual use are more likely to experience corrugation and overall wear. Rail grinders are used to grind the tracks when rail corrugation is present, or before corrugation begins to form on the tracks. Major freight train tracks use rail grinders for track maintenance based on the interval of tonnage, rather than time. Transit systems and subways in major cities continue to use scheduled rail grinding processes to combat the corrugation common to heavily used tracks. Rail-grinding equipment may be mounted on a single self-propelled vehicle or on a dedicated rail-grinding train which, when used on an extensive network, may include crew quarters. The grinding wheels, of which there may be more than 100, are set at controlled angles to restore the track to its correct profile.

The machines have been in use in North America, the United Kingdom and Europe since the early 20th century. They are made by specialist rail maintenance companies who may also operate them under contract.

The early 2000s saw several advancements in rail maintenance technology, most notably the introduction of track reprofiling by rail milling trains for which advantages in accuracy of the profile and quality of the processed surface are claimed. A second technology that is gaining widespread acceptance in Europe, Germany in particular, is high-speed grinding. While it cannot reprofile rails like milling or other grinding trains, its working speed of approximately 80 km/h allows defect removal and prevention to be achieved with little or no impact on other scheduled traffic.