Sakura Kinomoto is a girl of 10 years, student of the fictional Japanese city of Tomoeda who accidentally opens a mysterious book called Clow Book. Book 52 magic cards taken out by a wind storm caused by the magic of the letter Wind, which was released when Sakura read your name. Kerberos, the guardian of the cards (much like a creature with a very small stuffed animal), emerges from the book and tells Sakura that the letters were scattered throughout Tomoeda and it is his duty to capture them again, making it a cardcaptor (capturing of letters in English).
The letters cause strange phenomena around Sakura, which employs the powers of the letters captured in his magical staff to master them and attach them to your collection. She enlists the help of her friend Tomoyo, and later other characters Syaoran Li as a rival cardcaptor who later becomes his ally, and Yue, another guardian of the cards.
Throughout the plot, beyond the mysterious stories surrounding the letters are also present scenes that show the growing romance between Syaoran and Sakura, interspersed with the action scenes.
In the second half of the story, there are new characters, as Hiiragizawa Eriol and Sakura begins to transform the Clow Cards in their own letters: Letters Sakura (Sakura Cards).
The Clow Cards are magical objects, but somehow also living beings with feelings and personalities, created by a powerful sorcerer known as Clow Reed (or Clow Reed), with a mix of Western and Eastern magic. Are able to perform amazing effects in unlimited quantity, but each letter is related to a single power or strength. They can also manifest itself in a semi-human (or, in some letters, an animal or object), which somehow reflects your personality.
To contain the power of these letters after his "death", the Magician Clow confined them in a book and presented to the two entities created (Kerberos and Yue) the mission of protecting them. For many years, the cards would have remained at rest and the book of Clow gone through several owners who were unable to open it, to be opened by Sakura, with the consequent release of the letters.
In total there are 19 letters in the manga and anime in 52, not including the letter Sakura The Hope (Hope) and Clow card The Nothing (vacuum), both from the 2nd movie. There are cards you do not see being captured in the anime, as The Arrow (Arrow, captured in the 1st film in the series), The Through (Through) The Bubbles (Bubbles), The Libra (Libra), The Wave (Wave).