A level crossing (a primarily British term; usually called a railroad crossing in the United States) occurs where a railway line is intersected by a road or path on one level, without recourse to a bridge or tunnel. It is a type of at-grade intersection. The term also applies when a light rail line with separate right-of-way or reserved track crosses a road in the same fashion. Other names include railway crossing, grade crossing, road through railroad, or train crossing.

Early level crossings had a flagman in a nearby booth who would, on the approach of a train, wave a red flag or lantern to stop all traffic and clear the tracks. Manual or electrical closable gates that barricaded the roadway were later introduced. The gates were intended to be a complete barrier against intrusion of any road traffic onto the railway. In the early days of the railways much road traffic was horsedrawn or included livestock. It was thus necessary to provide a real barrier. Thus, crossing gates, when closed to road traffic, crossed the entire width of the road. When opened to allow road users to cross the line, the gates were swung across the width of the railway, preventing any pedestrians or animals getting onto the line. The first U.S. patent for such crossing gates was awarded on 27 August 1867, to J. Nason and J. F. Wilson, both of Boston.