It is generally appreciated that warm weather negatively affects marathon running performance. This brief review summarises the historical literature on this topic and recent work that our laboratory has performed to quantify the impact of weather on marathon running performance. Using 140 race-years of data, we have demonstrated that marathon performance times slow progressively as weather warms above 5-10 degrees C wet bulb globe temperature, that men and women are affected similarly, but slower runners suffer a greater performance penalty than elite runners. The recent generation of a nomogram that predicts changes in finishing time consequent to changes in weather conditions offers runners and coaches a tool for use in developing marathon race strategy.