In the not-so-distant future, around the year 2400, humanity sets its sights on Mars with an ambitious goal: to transform it into a habitable planet. Giant corporations, sponsored by the World Government on Earth, embark on massive projects to raise the temperature, oxygen levels, and ocean coverage until the environment becomes suitable. In Terraforming Mars, you play as one of these corporations, working together in the terraforming process, but fiercely competing for victory points. These points come not only from your contribution to making Mars green but also from advancing human infrastructure throughout the solar system and achieving other commendable feats.

During the game, you acquire unique project cards – there are over two hundred different ones! – by buying them into your hand. These cards can provide immediate bonuses, increase your resource production, or even introduce life to the planet. Many of them have specific requirements, becoming playable only when the temperature, oxygen, or ocean coverage reach certain levels. Buying cards is an investment, so the challenge is to balance acquiring them with actually playing them. Standard Projects are always available to complement your options.

Your basic income and score are determined by your Terraform Rating, which increases as you advance the global parameters. However, your production boosts your income, and many other factors generate victory points. You manage your resources (MegaCredits, Steel, Titanium, Plants, Energy, and Heat) on your player board. On the main game board, the competition is for strategically placing your city tiles, ocean tiles, and greenery tiles. Milestones and Awards are also worth many victory points.

Each round, called a Generation, follows a clear flow: player order shifts, the research phase allows you to buy new cards, and the action phase is where the magic happens. Players take turns performing one or two actions, such as playing a card, claiming a Milestone, funding an Award, using a Standard Project, converting plants into greenery tiles (thereby raising oxygen), or converting heat into a temperature increase. The round continues until all players pass, and then comes the production phase. When the three global parameters (temperature, oxygen, and oceans) have all reached their required levels, terraforming is complete, and the game ends after that generation. The winner is the corporation with the most victory points!