André Chapelon (26 October 1892 – 22 July 1978) was a noted French mechanical engineer and designer of advanced steam locomotives.
A graduate engineer of Ecole Centrale Paris, he was one of very few locomotive designers who brought a rigorous scientific method to their design, and he sought to apply up-to-date knowledge and theories in subjects such as thermodynamics and gas/fluid flow to the field.
Chapelon's work was an early example of what would later be called modern steam and influenced the work of many later designers of such locomotives (such as that of Livio Dante Porta).