EVE Online was the first MMORPG to attempt to create a "closed" economy; the closed economy was eventually dismantled, because it couldn't accommodate new players cleanly or easily, and favored established characters a bit too much. However, most of the tools used to support the closed economy still remain and one of the major ones is the Market, which acts like a "stock ticker" on commodities throughout EVE Online's entire community, giving commodity prices and demands for same throughout the entire game.

This market, more than anything else, is what replaces the need to do missions. There is always demand for commodities, the demand for the commodities is reflected in the EVE Online market, and there are always risk/reward trade offs.

The way these Markets work, a given node (either player character driven or computer driven) will post a price for a given commodity. If you produce that commodity, you can attempt to be the first shipment there to get the price - as multiple instances of the same commodity come in, the price drops, with factors contingent on how short the route is between the demand and the supply, and how risky the route is - if you have to route through a couple of zero zero systems (where there is no enforcement of law by the game) you run the risk of being hit by pirates run by other players - this is EVE's version of Player versus Player combat, and it runs in graduated zones from 0.0 to 1.0 (where 1.0 means that it's almost impossible for player on player action to begin.)

Beyond the straightforward market mechanic here, EVE Online markets also support player to player contracts for commodities and work agreements. You start out able to have one outstanding contract; each skill level of the Contracting skill adds three to the total, with a maximum of 16 for skill level 5. An outstanding Contract on the Market means you're available to take on the job. Contracts players (and player corporations) can put on the market include auctions, item exchange, loans and courier duty. Corporation Contracts allow corporations (the EVE equivalent of guilds on other games) to put work offers out for members and non members (and other corporations) to meet, allowing the resource exploitation and manufacturing model to extend in ways that add significant play depth.

To create a contract with the EVE Online market tools, you'll need to put up 100,000 ISK as a deposit to put up a public contract; this is also used to pay for the work done.