A train seat is a seat used in a passenger train's passenger railroad car allowing passengers to sit during their travels.

A train seat design has a seat base height, seating angle, seat depth (the distance from the front edge of the seat to the back of the seat), seat hardness and seat width that can support the sitting position of average passengers. The seats generally have paddings or are cushioned, providing a level of comfort to the passengers and distributing the sitting passenger's weight. The chairs generally are equipped with armrests and neck support at a height of the average passenger. At the back of a chair often flip-down tables, magazine racks and waste containers are installed for passengers behind them. More luxurious railroad coaches like lounge cars can provide recliners with special upholstery with amenities like headphone connections and electronic visual displays are the like.

To use the available space in an optimal way often also jump seats are installed that only take up space when a passenger sits on it. When nobody uses them there's extra space for bicycles, strollers and the like. These seats are generally installed near the doors, which means at stops passengers who wish to continue using these seats will have to stand up to make room for passengers who want to leave the train.

Train passenger coaches can have different seating layouts, based on the coach's maximum seating capacity, that determine the placement of the train seats, space for walking and legroom for the passengers. In a corridor coach there are several compartments with generally two times three seats facing each other. The chairs in an open coach, with one or more open plan areas with a centre aisle, are usually arranged in pairs of two with an aisle seat and a window seat. In a composite coach are mixed-class cars featuring both open seating and compartments. Some seats, generally close to the train doors, are designated as priority seats for elderly, disabled, pregnant women and the injured. In first class coaches individual seat arrangements with more legroom are provided for. The chairs are not necessarily facing the direction that the train is travelling as trains change direction and often sets of seats are arranged facing each other with a single or double tables in between.

Long seats or longitudinal seats refers to a layout in which bench seats are installed along the side walls of the train car. This configuration minimizes seating space to maximize standing room, allowing for smoother boarding and alighting of passengers. Since this style emphasizes transportation volume above all else, it is often used for rapid transit within cities, commuter rails and lines of a similar nature.

Cross seats or transverse seats refers to seats oriented across the width of the car. Since this style emphasizes passenger comfort, it is often used for long-distance inter-city routes, high-speed rails, and tourist railways. Cross seats can be classified into fixed cross seats, rotating cross seats, and flip-over cross seats. Fixed cross seats include box seats and fixed unidirectional seats.

In some countries, such as Japan, the alignment of seat pitch and window placement is considered integral in cars with cross seat. Designs also must consider factors such as seat rotation and table deployment from the walls.

On routes with a high number of tourists, cross seat is preferred over long seat. This creates a challenge in balancing tourism-oriented transport with regular commuting needs.