Volcanic activity can have a notable impact on glacier behaviour (dimensions and dynamics). This is evident from the palaeo-record, but is often difficult to observe for modern glaciers. However, documenting and, if possible, quantifying volcanic impacts on modern glaciers is important if we are to predict their future behaviour (including crucial ice masses such as the West Antarctic Ice Sheet) and to monitor and mitigate glacio-volcanic hazards such as floods (including jökulhlaups) and lahars. This review provides an assessment of volcanic impacts on the behaviour of modern glaciers (since AD 1800) by presenting and summarising a global dataset of documented examples. The study reveals that shorter-term (days-to-months) impacts are typically destructive, while longer-term (years-to-decades) are more likely protective (e.g., limiting climatically driven ice loss). However, because these events are difficult to observe, particularly before the widespread availability of global satellite data, their frequency and importance are likely underestimated. The study also highlights that because the frequency and nature of volcano-glacier interactions may change with time (e.g., glacier retreat may lead to an increase in explosive volcanic activity), predicting their future importance is difficult. Fortunately, over coming years, continued improvements in remotely sensed data will increase the frequency, and enhance the quality, of observations of volcanic impacts on glaciers, allowing an improved understanding of their past and future operation.