Runes are small stones inscribed with magical glyphs that can be inserted into Socketed Items. Runes are different from other Insertable Items: not only do individual Runes have set magical properties, certain combinations (or Rune Words), when inserted into an item in the proper order, give that item even more wondrous abilities.

Runes can be used to create Crafted Items.

Common Runes
Runes are listed from most common to least common: El, Eld, Tir, Nef, Eth, Ith, Tal, Ral, Ort, Amn, Shael, and Thul are pretty common. You receive Ral, Ort and Tal as a quest reward in Act V. You shouldn't trade much for them since you can find them pretty easily with regular play. Don't fall for the "1 Shael or/+ Amn for 1 SOJ" scam. You can find these yourself. If you're thinking of freeing up space, throw those Runes away and save all Runes from Sol through Zod.

Semi-Rare Runes
Listed from most common to most rare: Sol, Dol, Hel, Io, Lum, Ko, Fal, Lem, Pul, Um. Some of these Runes are more valuable than others depending on their stats and how they are used in Rune Words or Crafted Recipes.

Extremely Rare Runes
Listed from most common to most rare: Mal, Ist, Gul, Vex, Ohm, Lo, Sur, Ber, Jah, Cham, Zod. Trade these for good stuff!

Rune Words
If the player puts certain combinations of Runes in the correct order into an item with exactly that number of sockets and of the correct item type, the item's name will change into a "unique" name, displayed in gold, and the item will acquire extra powers, depending on the "rune word" that was used.