The Belgian railway line 37 is a railway line in Belgium connecting Liège to Aachen in Germany. Completed in 1843, the line runs 47.4 km in Belgium. and another 6.8 km in Germany. It is the first and oldest cross-border railway line worldwide. Since 2009, high speed trains running between Brussels and Aachen use the HSL 3 instead of the line 37 between Chênée and Hergenrath.