- This article refers to the planet Z'ha'dum. For the Season 3 episode, see: Z'ha'dum (episode).
"If you go to Z'ha'dum, you will die."
- – Kosh
Z'ha'dum's official Earth Alliance designation is Alpha Omega III, meaning it is the third planet of its star. The planet is located on the rim of known space. It is approximately a four day jump from the Epsilon Eridani system.
Z'ha'dum is covered in extensive mountain ranges. The temperature averages 50 degrees Fahrenheit and the gravity is approximately 1.3G. The mountains are made of igneous rock and the plains of sedimentary rock. Violent dust storms cloak roughly 25% of the planetary surface at any one time. The planet has an extremely dry atmosphere with low levels of carbon monoxide, which would prove fatal to humans within about an hour. There is also a background level of radiation, suggesting the planet was nuked approximately one thousand years ago.
Stone pillars ranging from 100 to 150 yards in height cover most of the planetary surface. They are spaced exactly 2.43 miles apart from one another. The pillars are covered in characters from the Shadow language.
By the twenty-third century, Z'ha'dum was a blasted, charred wasteland, its surface marred by the many attacks that drove the Shadows away from the planet eon after eon. When they returned at the dawning of the Third Age, their cities were kept mostly underground.
"Z'ha'dum is the homeworld of the Shadows. No one leaves the same as they arrived."
- – Delenn
It is unknown if Z'ha'dum was the homeworld of the Shadows as a species, but for most of their long history they considered it their home. This was due to the presence of Lorien, one of the First Ones, who lived in a deep chasm on the planet for over one million years.
The last time the Shadows would be driven from the planet would be at the end of the First Shadow War, in roughly the thirteenth century A.D. Some of their race managed to remain, but were in a state of hibernation. One thousand years later, during the Babylon Project's early days, the Shadows returned. They slowly rebuilt their great cities. They also began to recall some of the ships that they had hidden throughout the galaxy after the War.
One of their ships had been hidden on Mars. When Earthforce crews uncovered it, they reactivated an ancient beacon. Days later, the Shadows sent a second ship to retrieve the first one. The Psi Corps, however, had managed to plant a homing beacon inside. In 2257, Interplanetary Expeditions was commissioned to send a ship (the Icarus) to Z'ha'dum on an exploratory mission--most of the crew was apparently unaware they were being used, that the planet was where the Shadow vessels had been tracked to. When the Icarus arrived on Z'ha'dum, they found it seemingly deserted. They quickly awoke some of the Shadows, however, and those members of the crew who would not serve willingly were said to have been killed. However, Morden and Anna Sheridan were "enslaved" by the Shadows.  It is possible that the other crew members were simply integrated into various Shadow vessels to fight in the upcoming war.
Third Age of Mankind
Once the shadows had been defeated and left for beyond the rim, the White Star went to investigate Z'ha'dum, only to see a mysterious fleet (almost certainly the Drakh) leaving Z'ha'dum moments before the entire planet exploded. 
- According to JMS, the name "Z'ha'dum" is of Minbari origin and roughly translates as "Death of the future", while the novel The Shadow Within (considered mostly canon) which details the story of the Icarus and its voyage to Z'ha'dum reveals that the Earth codename for the mysterious planet is "Alpha Omega 3". Alpha and Omega, when used together can often refer to the "beginning and the end" or the "beginning of the end" as they are the first and last letters in the Greek alphabet, respectively. So it appears that both the Minbari and Human name for this world mean roughly the same thing.