The Grimmerie (known on Earth as The Lesser Key of Solomon the King) is a book of powerful magic which Elphaba finds in the attic of Kiamo Ko and was later given to her by Sarima. Elphaba can only read parts of it, as the book originates from the other world (our world). The book also created Yackle to be a guardian to the book and a witness to the life of Elphaba.
In the musical, it's Elphaba's book of spells, given to her by the Wizard's press secretary, Madame Morrible. Elphaba used it to put wings for the Winged Monkeys, make her broom-stick levitate, enchant Nessarose's shoes, save Boq's life by turning him into the Tin Man, and save Fiyero's life by turning him into the Scarecrow.
In the novel, it is strongly suggested that it is a grimoire from our world which a powerful sorcerer took to Oz sometime in the distant past. In A Lion Among Men, it is revealed that Yackle is the guardian of the Grimmerie and was created from it.
The Wizard is in search of the Grimmerie, which had been hidden in Kiamo Ko and had entered into the ownership of the Tigelaar family. It was given to Elphaba Thropp by Sarima, who had no need for it as she couldn't read. It is further substantiated that the book comes from Earth rather than Oz in that those of pure Ozian ancestry can't read it whereas Elphaba-who is half-Munchkin, half Earthling- can only read fragments.
The Wizard sought to bargain with Elphaba for the Grimmerie in exchange for Nor. This she did not allow, and it is revealed that, later, he asked Dorothy Gale to take the book if she could. Since it was too heavy, she was unable to do so. In A Lion Among Men, the Grimmerie had been secreted into the Clock of the Time Dragon, while a wayward page had been used by Emperor Shell to create dragons.
In Out of Oz, Glinda comes into posession of the Grimmerie when the Clock of the Time Dragon comes to Mockbeggar Hall. Glinda then--with the help of Elphaba's granddaughter Rain--uses the book to impede General Cherrystone's progress across Restwater Lake.
Eventually, as the battle progresses between Munchkinland and Loyal Oz, Mombey uses the books information on the training of Dragons to attack the Emerald City, successfully ending the war. After failing to bring Liir back from his Animal form, Mombey attempts to use the Grimmerie to "call the lost forward." In doing so, she reveals Ozma Tippetarius as well as Rain's green skin.
At the end of the novel, Rain takes the Grimmerie and--using the broom--flies out past the Thousand Year Grasslands and an expanse of desert to the ocean. She then continues to fly over the sea, vowing to drop the book into its depths.
In Wicked the Musical, the Grimmerie is a spell-book, apparently from the land of Oz, which is in the Wizard's possession. Despite it being from the land of Oz, only Elphaba and Nessarose are capable of reading it: contrary to the book, the Wizard is unable to read it. Though the musical is unclear as to what purpose it really serves besides being "a recipe book for change", it can be concluded that The Wizard wants to use it to give himself real power as opposed to his current condition.
At the climax of Act 2, Elphaba gives the Grimmerie to Glinda, despite her stating that she cannot read it.
The Levitation Spell I
Used by Elphaba to unwittingly give wings to the Wizard's monkey servants.
Ahben Tahkay Ahben Tahkay Ahben Atum Ahben Takayah Entayah Ah Entayah Tifentah Ahben Tahkay Ah
In the San Francisco tryouts, this was followed by more chanting which was deleted for the Broadway show.
Et Antay Daytum Entayah Tahkay Bayah Ben
The Levitation Spell II
Used by Elphaba to enchant the broom and fly.
Ahben Tahkay Ah Tum Entay Ditum Entayah (repeated)
According to MusicalSchwartz.com, however, this spell is as follows.
Ah May Ah Tay Ah Tum Ditum
The Motion Spell
Used by Elphaba on the silver slippers to allow Nessarose to walk. It changes them from silver to red, enchanting them. Ambulahn Dare Pahto Pahpoot Ambulahn Dasca Caldapess Lahfenahto Lahfenahtum Pede Pede Caldapess (repeated)
The Love Spell
The incomplete spell used by Nessarose in an attempt to make Boq "lose his heart" to her.
Ah Tum Core Tum Ah Tum Tah Tayk-
The Tin-Man Transformation
Used by Elphaba to allow Boq to live without a heart.
Vivahlos Vivahlos Meno Non Cordo Meno Vivahlos Vivahlos Meno Non Cordo
The Scarecrow Transformation
Used by Elphaba to save Fiyero, unwittingly turning him into a Scarecrow in No Good Deed.
Eleka Nahmen Nahmen Ah Tum Ah Tum Eleka Nahmen (repeated)
The original chant Schwartz was planning to use was as follows.
Ad Nay Prae Tum Ister Fah Tum Antay Dayculum