山径越野跑是一种在小径上跑步与徒步的运动。它和公路跑与场地跑的区别在于，跑者主要是在徒步小径上跑步，通常会经过山地，可能出现较大起伏。中文的“越野跑”通常指trail running，也称作“山径越野跑”或者“跑山”，这一类的越野跑比赛中一般会出现40公里以上的长距离赛道。同时，“越野跑”在中文里也可用来指田径越野跑（cross country running），它是一项国际田联赛事，通常赛道较短，不超过12公里，规则比山径越野跑要严格。

越野跑的参与人数正在逐年上升。从2006年到2012年美国的越野跑人数从450万上升到了600万。 不仅北美拥有上百个越野跑赛事，全世界的越野跑赛事的数量也在最近几年迅速增长。 很多人比起公路跑来更偏爱越野跑，主要原因一是越野跑的压力会更小，另一方面是越野跑可以与自然环境接触。 走向自然的潮流，也使得最近五年内，一些非常规的越野马拉松和探索性比赛的参与者迅速增加。

Trail running is a sport which consists of running and hiking over trails. In the United Kingdom and Ireland it is called mountain or fell running. It differs from road running and track running in that it generally takes place on hiking trails, often in mountainous terrain, where there can be much larger ascents and descents. It is difficult to definitively distinguish trail running from cross country running. In general, however, cross country is an IAAF governed discipline that is typically raced over shorter distances (rarely over 12 kilometers), whereas trail running is loosely governed, and run over longer routes.