The currency in  Path of Exile is presented in the form of various items, and the whole economy is based on exchanging this orbs between players.

Currency can be used not only in trade, but also in crafting. So each orb has its own unique properties when used on the item or gives some other useful properties to the character.
For example, if you buy chaos orb, it will randomly change all modifiers at your item.  However, an exalted orb will give your item a new random affix.

The most used orbs for trading with other players are orb of chaos, orb of exalt and alchemy orb. All trading in the game is based on these three currencies; other orbs are used less often.

Mostly these are items that can be used to craft equipment and other stuff.

Poe Currency can be divided into the next 10 types:

  1. Orbs
  2. Splinters
  3. Essences
  4. Prophecies
  5. Vials
  6. Harbinger orbs
  7. Perandus coins
  8. Delve orbs
  9. Oils
  10. Catalysts

In Exile Path you can also find seasonal items, such as Harbinger’s Orb and Delirium Orb, which were added in the corresponding updates.

Overall the currency systems includes a vast number of orbs, scrolls, coins and other items.

The most valuable poe orb is the Mirror of Kalandra.