Shadow Magic was the art shadow manipulation, it is believed to have been relatively common in the provinces Hammerfell, High Rock and Skyrim during the Third Era. Azra Nightwielder was the very first Shadowmage.
Shadow Magic was said to have had the power to change the past, present, and future. It was powerful enough to rival even the legendary Elder Scrolls.
Shadow Magic could be used to create Shadow Gates, that could be opened using Shadowkeys. Shadows could be absorbed to strengthen one's self, or could be molded in to physical forms, such as weapons. Shadow Magic could also be used to visit other realms, to assist alternative versions of yourself and request their aid.
Shadowmages could, however, be twisted by the very nature of the Shadow Magic, and for that reason Shadowmages were largely distrusted.
After the discovery of shadow properties, Azra Nightwielder tried to merge all the possible worlds created by shadows in to one, so he would exist in all world. His ritual was stopped by Redguard soldiers, who feared his power. Azra lost control of the magic, and it caused an explosion. A crater remained that could still be seen at Azra's Crossing.
Shadow Magic also played an important role in the War of Bend'r-Mahk, which created an entity known as Umbra' Keth, or the Shadow of Conflict. Multiple parties, such as Jagar Tharn and Pergan Asuul, attempted to gain control of the shadow. But he Hero of Conflict, being assisted by Skelos Undriel, survived Azra Nightwielder, and was able to collect the Star Teeth to destroy the Umbra' Keth and defeat Pergan Asuul.