He's the life of the party and she prefers to stay home and read a book. She is a clean freak, his dorm room is a disaster. Though opposites clearly attract, having staying power in a relationship is another issue entirely. Personalities that mesh well in the long term are usually complementary rather than opposite.

Introverted and Extroverted

Introverts need time alone when feeling overwhelmed, while extroverts prefer to be in the company of people. These two types of personalities can be a great match as long as you appreciate each other's differences, advise social workers Linda and Charlie Bloom in the Psychology Today article "Why Introverts and Extroverts Attract Each Other." If your boyfriend is outgoing and you are a quiet bookworm, he will keep your social life humming while you introduce him to the world of creativity and the arts.

High Strung and Laid Back

If you prefer hanging out with friends and don't stress too much about school, while your girlfriend is a straight-A student, head cheerleader and student council president, you and she could be what anthropologist Helen Fisher calls a "negotiator" and a "director." Fisher, who bases her research on brain chemicals, says that the focused and logical director is perfectly matched to the imaginative and social negotiator. Your laid-back attitude probably helps her relax, while her driven nature might spur you to become more goal oriented.

Risk Taker and Cautious Observer

Risk takers constantly push limits, while cautious observers stand back and assess the situation. These two personalities are dubbed the "explorer" and the "builder" by Fisher, and are another good match because each mellows out the extremes in the other's personality. Your risk-taking boyfriend might show you the fun of rock climbing; your cautious nature will make sure you avoid a treacherous climb. Having vastly different perspectives on life keeps you both balanced -- as long as you agree to compromise when your opinions clash.

Similar Personalities

Sometimes the best-matched personalities are those that are similar, notes the Science of Relationships article "Do Opposites Attract?" In the study "Do People Know What They Want: A Similar or Complementary Partner?" published in the journal "Evolutionary Psychology," 760 college-educated singles confirmed this notion, as most preferred a partner with a personality close to their own. Partners who are too different may have trouble understanding each other or may start to rely on each other to compensate for areas of weakness -- without developing skills to cope on their own. For example, a shy partner might let an outgoing partner do all the talking in social situations and never learn to speak up on his own. In contrast, if both you and your girlfriend are sociable and laid back, not only will you easily understand each other, but you won't have to make as many compromises -- because you both like doing the same things.