The in-game economy in "Eve Online" is an open economy that is largely player-driven. Non-player character (NPC) merchants sell skill books used by players to learn new skills and blueprints to manufacture ships and modules. NPC merchants also buy and sell Trade Goods. Some Trade Goods are only for trade between NPC merchants while others have a functional use and are not good for trade with NPCs. The characters themselves gather the necessary raw materials to manufacture almost all of the ships and ship modules in the game. NPC ships can be looted and salvaged for items and materials. Non-player created ships and equipment may be purchased from various NPC factions as a character gains status with them, and can be resold in the in-game economy. The in-game currency is ISK (Interstellar Kredits), which is also the currency code of the Icelandic króna, the real-world currency of Iceland, where the "Eve Online" development studio is located.