GrailQuest is a series of gamebooks by J. H. Brennan. The books are illustrated by John Higgins. The stories follow the adventures of a young hero named Pip, who is often called upon by Merlin to right wrongs and save the realm from evil. The series is light in tone and does not take itself seriously, often spoofing the fantasy genre and inserting slapstick humour or nonsensical elements.

The series is mostly set in the realm of Avalon, although the fourth volume, Voyage of Terror, takes place almost entirely in ancient Greece, after Merlin's summoning spell goes wrong. While there were eight total books published in the series, books seven and eight were never published in the United States.

The rules of GrailQuest are quite simple when compared to most RPGs. The player must roll two six-sided dice and add the results. If the result exceeds 6 (which will happen 58.3% of the time), then the enemy is injured and loses a number of Life Points - how much depends on what the dice shows, as every point over 6 will count as a point of damage. When a character's Life Points reach zero, the character is dead, and when they are at 5, they are knocked out.

If wielding a weapon, the number needed to hit may be lower, and extra damage will usually be inflicted. For instance, Excalibur Junior hits on a roll of 4 (hitting 91.7% of the time) and provides a bonus 5 points of damage. There is no defence roll, but damage is reduced by a set amount by any armour the character is wearing.

Initiative is determined by an initial, opposed roll where the highest roll gets the first attack. From then on, the character and the enemy take turns to attack. Surprise is sometimes involved (for example, in Gateway of Doom, a giant spider gets first strike automatically due to Pip being in its home territory).

If the character dies, the player must go to section 14, which describes his afterdeath and tells him to calculate his Life Points again. Merlin then resurrects Pip, who has to start from the beginning of the adventure again - although some books will only require him to start from a certain point; for example, Gateway of Doom allows Pip to restart at the beginning of the Ghastly Kingdom of the Dead, and Realm of Chaos allows him to start from the beginning of a certain location. However, all previously killed enemies remain dead, and any treasure the player found is gone for good. (In some books, killed enemies return to life with half the Life Points they had the first time around.)

In the inaugural issue of The Games Machine, John Woods thought the books had a "pleasant light-hearted feel." He also noted that Grailquest books required a lot of skill, as opposed to the large element of random chance required in the rival Fighting Fantasy book series. Woods thought that Grailquest should have done as well or even better than Fighting Fantasy, but speculated that perhaps players "preferred the hectic hack-and-slay action of Fighting Fantasy to the more leisurely and lengthy descriptive sections of Grailquest."

In 2012 the company Tin Man Games planned to create iOS and Android versions of the books.