"There are no contest in the Art of Peace. A true warrior is invincible because he or she contest with nothing. Defeat means to defeat the mind of contention that we harbor within. "

What is Aikido?                                                                    

      Emerging from a long period of obscurity in the East aikido has been called one of the most subtle and sophisticated of the martial arts, and an effective discipline for the development, integration, and utilization of all man's powers, physical and mental (spiritual).

      What may appear at first glance to be a unique method for efficiently defending yourself against any form or type of attack will reveal itself under careful to be not only an effective method of self-defense derived from Japanese Bujutsu (warrior arts); in addition it is a discipline of coordination, a way of strengthening the mind and body, of fusing the individual's physical and mental powers so that he or she will emerge as a more fully integrated human being. The word in fact, means, "method or way (do) for the coordination or harmony (ai) of mental energy (ki)."

      The particular martial art method developed by O'Sensei Morihei Ueshiba which he reffered to as "aikido" combines practical self-defense movements taken from sword and spear fighting, jujutsu, aikijutsu and other ancient, more esoteric forms of martial arts -- with an emphasis from the very first moment of of practice upon a characteristic centralization of thought and action, and the extension of mental energy or ki that makes this such an intriguing art.

Can AIKIDO be Used for Self Defense

"Those who are skilled in combat do not become angered,
those who are skilled at winning do not become afraid.
Thus the wise win before the fight, while the ignorant fight to win."

Yes, Aikido can be a very effective form of self-defense However, it can take considerable time and effort before Aikido (or any martial art) can be used effectively in a self-defense situation.

From:  http://www.aikidofaq.com/introduction.html