The Clow Book is a book containing a collection of mysterious and powerful magic cards titled "Clow Cards". originally owned by Clow Reed. It is first seen on Episode 1 when Sakura Kinomoto goes inside of their house's basement after hearing a loud noise coming from the basement.
The book's cover is designed as a golden lion named Cerberus which is the guardian of the Clow Cards. When Sakura opened it, she first saw The Windy card, and she reads its name loud, causing the cards to escape the Clow Book where they are scattered all over the city.
Meanwhile, Cerberus takes material form in his disguise of a plush toy or stuffed animal, after awakening from his deep sleep and upon realizing what's happening, appoints Sakura as the Card Captor, the one who will recapture the Clow Cards.
The Clow book has it's own arrangement of cards. The total number of cards is "52", which means The Nothing and The Nameless card, together with The Hope card, are not one of the official Clow cards, and The Nameless and The Hope card do exist in Sakura Cards, and not in Clow Cards.
This is the list of Clow Cards based on the official arrangement. This list also shows the order in which the Clow Cards are re-captured in the anime:
In season three, the Clow Book loses its original appearance and turns pink with the name "Sakura" on the front of the book.
Bandai and Clamp ProductClamp's Clow Book was released back in 2001, however the Clow Book resembles more of a box than a real book. The cards inside do not resemble their anime counterpart.
Bandai's Official Clow Book was released in 2002. This Clow Book looks and feels like a real book. It also includes a real clasp on the side. The cards inside strongly resemble the anime's Clow Cards.