Terraforming

Terraforming is the process of reshaping or otherwise modifying the ecology of a planet or moon to make it more habitable for humanoid life.

Federation terraforming projects

Mars - as of 2155, conditions on Mars were sufficiently altered to allow Humans to survive on the surface with just a small breathing gear and thermal insulation. (ENT: "Terra Prime")
Caldos colony - established in the 22nd century. (TNG: "Sub Rosa")
Genesis Planet - created and destroyed in 2285 as a result of the Genesis Device. (Star Trek III: The Search for Spock)
Venus - as of the 24th century several terraforming stations were located on Venus. (DS9: "Past Tense, Part I")
Velara III - abandoned in 2364
Browder IV - The starships Hood and Enterprise-D assisted with the terraforming project here in 2366. (TNG: "Allegiance")
New Halana
Blue Horizon
Regula