Comfort is defined as the well-being of an individual in relation to a particular environment. Ride quality is a concept relating to a passenger's judgement of his comfort when travelling. The representation of experimental data from research conducted on comfort when travelling by rail is discussed. Origins of discomfort include longitudinal acceleration, lateral acceleration, vertical acceleration, roll speed, roll acceleration, jerk, peak-to-peak acceleration, and mean acceleration. Methods for evaluating comfort are described. The general development of comfort as a function of train speed and tilting is discussed.