In the 2400s, mankind starts to terraform the planet Mars. Giant corporations, sponsored by the World Government on Earth, start huge projects to raise the temperature, the oxygen level, and the ocean coverage until the environment is habitable. In Terraforming Mars, you play one of those corporations and work together in the terraforming process, but compete for gaining victory points that are awarded not only for your contribution to the terraforming, but also for increasing human infrastructure throughout the solar system, and doing other commendable things. The players obtain unique project cards (from over two hundred different ones) by buying them to their hand. The projects (cards) can represent multiple things from introducing plant life or animals, hurling asteroids at the surface, building cities, to mining the moons of Jupiter and establishing greenhouse gas industries to warm up the atmosphere. The cards can provide you immediate bonuses, as well as increasing your production of different resources. Many cards also have requirements and they come into play when the temperature, oxygen, or ocean coverage increases enough. Buying cards is expensive, so there is a balance between buying cards (3 megacredits per card) and actually playing them (which can cost anything between 0 to 41 megacredits, depending on the project). Standard Projects are always available to assist your cards. Your basic income, as well as your basic score, is set on your Terraform Rating (starting at 20), which goes up every time you raise one of the three global parameters. However, your income is tied to your production, and you also get VPs from many other sources. Each player tracks their production and resources on their player boards, and the game uses 6 types of resources: MegaCredits, Steel, Titanium, Plants, Energy, and Heat. On the game board, you play for the best places for your city tiles, ocean tiles, and greenery tiles. You also compete for unique Milestones and Awards worth many VPs. Each round is called a generation (guess why) and has the following phases:

1. Player order moves clockwise.
2. Research phase: All players buy cards from 4 privately drawn.
3. Action phase: Players take turns doing 1-2 actions from these options: Playing a card, claiming a Milestone, funding an Award, using a Standard project, changing plant into greenery tiles (and raising oxygen), converting heat into a temperature raise, and using the action of a card in play. Turns continue around the table (sometimes several laps) until all players have passed.
4. Production phase: Players receive resources according to their terraform rating and production parameters. When the three global parameters (temperature, oxygen, ocean) have all reached their goal, the terraforming is finish, and the game ends after that generation. Count your Terraform Rating and other VPs to decide the winning corporation!