Planeshifting

Planeshifting is the arcane art of transporting people and objects between planes. It is a key element of conjuration magic. Though the discipline is difficult to master, it can be used for a wide variety of purposes once unlocked.

Utility

Planeshifting is most famous as a means of transportation. The spell Plane Shift allows powerful magic users to instantly travel between runic transportation circles across planes. In recent centuries, the technology of these rune sequences has incorporated "detour sigils" that bounce users off mortal-resistant bubbles of the Liminal Plane, allowing "planeshifting" between destinations on the same plane as well.
The most mundane use of planeshifting is to store one's possessions in pocket dimensions. The fairly common Bag of Holding, for example, weaves a portal to a pocket dimension into an otherwise ordinary satchel to facilitate carrying more objects than would usually be practical. Spells such as Drawmij's Instant Summons and Leomund's Secret Chest utilize planeshifting to keep particular objects safe and easily transport them from one place to another.
Planeshifting can also be used for defensive purposes by displacing hostile creatures to other planes. Banishment is a key utility spell for defensive wizards, particularly those who often fight fiends and other creatures of extraplanar origin. It temporarily consigns its target to its native plane of existence (or, if used on the target's home plane, to a harmless demiplane). If its casting is sustained for a full minute and not resisted by the target, creatures native to other planes of existence will remain there indefinitely. In a more powerful and difficult-to-resist method of banishment, advanced magic users can use the spell Plane Shift to send targets to any teleportation circle whose rune sequence they know. Some mages collect rune sequences of circles in particularly remote and hostile places, known as banishment circles or sometimes punishment circles, specifically for this purpose.

"Sorry, Father. Death would be too easy."
—Nekrotzar Oakenheart, upon planeshifting his abusive father Agamemnon to a banishment circle in Stygia

The largest-scale use of planeshifting ever recorded was Xenomancer Arie Lutvigen's transportation of Hart Cove to the Ethereal Plane in Y1085.

Discovery

Some magical creatures possess innate planeshifting abilities. These are largely denizens of the Astral Plane, though a few primarily Material creatures (such as the phase spider) have limited affinity for planeshifting. This power was studied and harnessed by disciples of Hildegard in the Y200s Age of Complexity and has been refined in the centuries since.