Southern Alaska provides an ideal setting to assess how surface mass changes can influence crustal deformation and seismicity amidst rapid tectonic deformation. Since the end of the Little Ice Age, the glaciers of southern Alaska have undergone extensive wastage, retreating by kilometres and thinning by hundreds of metres. Superimposed on this are seasonal mass fluctuations due to snow accumulation and rainfall of up to metres of equivalent water height in fall and winter, followed by melting of gigatons of snow and ice in spring and summer and changes in permafrost. These processes produce stress changes in the solid Earth that modulate seismicity and promote failure on upper crustal faults. Here we quantify and review these effects and how they combine with tectonic loading to influence faulting in the south-east, St. Elias and south-west regions of mainland Alaska.