It's code in most areas that the entry door to an attached garage be “fire-rated” and have a self-closing device. The purpose is to keep a garage fire from spreading to the house. But don't worry—making this door self-closing is as simple as changing two or three of the door's hinges or installing a door closer at the top of the door. It'll cost about the same to go either route, and either is acceptable.
If you plan to use self-closing hinges, take the original middle hinge to your home center or lumberyard, and find self-closing hinges with plates the same size as the ones already on the door. You may have to chisel the edge of the door to get a new square-cornered hinge to fit in mortises machined for round-cornered hinges. Self-closing hinges look much like ordinary hinges except they have a bigger barrel to house the internal spring that makes them self-closing. Switch hinges one at a time so you won't have to remove the door, then wind and adjust the springs with the tools and instructions provided.
Door closers work well for odd or old doors that have hard-to-match hinges. They're also a good choice if existing trim won't allow for the extra thickness of the barrel found on self-closing hinges. You can mount them on either side of the door. Drilling templates and installation instructions come with the closer.
Whether you use a closer or self-closing hinges, adjust the mechanism so the door closes and latches on its own from a wide-open position.