Train spotting is a hobby that involves collecting sightings of trains. A train spotter will typically focus on a certain set of trains or moving stock — such as all cars of a certain model or all moving stock belonging to a particular company — and try to "spot" as many in that category as possible. Train spotters share information about the movements of trains with others and usually carry a data book in which they mark off the railway equipment they have spotted.

In addition to a data book, train spotters carry a notebook and pen or a tape recorder to note their sightings. Some also carry cell phones or pagers in order to communicate to other train spotters regarding the movement of trains. Some railway enthusiasts enjoy photographing trains as well.

In the modern world, the Internet has come to have a role in train spotting. Railway fans may maintain electronic records of trains they have spotted, and railway information can be kept up to date and made available to the community at large through the Internet. Train spotting websites allow fellow railfans to exchange information and cross reference sightings. The Internet has also made possible virtual train spotting, in which online pictures of trains are collected.

Train spotting requires a lot of patience and is often considered boring or pointless by outsiders. Railway workers may consider train spotters a nuisance, and law enforcement may view them as a security threat. Even other railfans, who indulge their love of trains through different methods, may deride train spotting.

Nevertheless, train spotting continues to be a popular hobby, with many websites, magazines, and other publications devoted to it. Train spotters are able to bond over their shared love of an activity that others do not understand, and some argue that they are beneficial to the railway system, as they may be able to spot problems on the track and prevent an accident.