Some of the Bretonnian Knights of the Realm decides to go on a Grail Quest. When on a Grail Quest the knight leaves his fief under the protection of a steward, his wife or one of his Household Knights, as he is usually far away from his home for years.
While on a Grail Quest, the Questing Knight travels the world on an attempt to prove himself. Not to the nation like on his Errantry Tour, but instead he needs to prove himself before the mighty guardian goddess of Bretonnia, the legendary Lady of the Lake. While on a Quest it is common to abandon the favored weapon of Bretonnian nobles, the lance. The lance is thought to represent his time as a Knight of the Realm, and is such generally only used by Questing Knights when doing something connected to his time as an ordinary knight. Instead, it is common to use heavier two-handed axes, maces,and claymores.
As he travels, he defends the land and fights injustice; constantly trying to get the attention of The Lady and testing himself beyond his limits. Sometimes the knight proves himself by doing some extraordinary feat, and The Lady will appear before him offering him to sip from the Holy Grail. At other times, however, the knight gets the attention of his goddess without some incredible test. If that is the case, the Green Knight will appear before the quester, challenging him to a duel.
When the Green Knight has been defeated, he will disappear back into the forest. The Green Knight will leave as if the wounds he recieved during the battle did not affect him, sometimes even picking up his severed head and walking away. Following that the Lady will then grant the knight a sip from the Grail, and he will be acknowledged as one of the legendary Grail Knights.