Mint is a wonderful herb that no kitchen (and therefore garden) should be without. It is also an important ingredient in Middle Eastern and Greek cuisine and, of course, in various iced summer drinks. However, in areas in which mint is perennial, it can creep farther than you'd like, crowding adjacent plants—especially when they're all in a container together.
The best way to control mint is to limit the spread of the plant's roots by planting it first in a pot, then sinking the pot into the ground or into the soil within a larger container. Every few weeks, give the pot a quarter turn to keep the roots from escaping through the drainage holes. When possible, use a plastic pot, which won't dry out as quickly as clay and will be easier to turn.