Credits are a form of currency utilized by the Terran Confederacy, Umojan Protectorate, Kel-Morian Combine and Terran Dominion – in essence, every major terran government of the Koprulu sector. They come in notes, coins, and round objects called "chips."
There are several types of currency, and traders can make money speculating on them.
Credits are used in the Wings of Liberty single player campaign to purchase unit and structure upgrades, and hire mercenaries. Credits are earned by completing missions (and sometimes from completing bonus objectives), except for the final Char missions, collecting more than twenty-five zerg research points, and collecting more than twenty-five protoss research points.
There are not enough credits on a single play-through to upgrade or hire everything. At one time there was a bug that once all missions were completed prior to the final Char missions, additional credits could be earned by replaying missions through the archive on any difficulty, but that has now been corrected by Blizzard Entertainment.
After a mission in which excess protoss or zerg research points are collected, they can be traded for credits by using the research console in the laboratory.
It is possible to gain a total of 2,030,000 credits from mission rewards and bonus objectives (including secret mission Piercing the Shroud), plus 250,000 credits from excess research points sold to Moebius Foundation, resulting in a total of 2,280,000 maximum credits per campaign playthrough.