The conventional 78-card deck is structured into two distinct sets, called the Minor Arcana and Major Arcana (arcana is the plural of the Latin word arcanum, meaning "hidden truth" or "secret knowledge"). Alternate names are the Minor Trumps and Major Trumps, or simply the Minors and the Trumps.
Tarot cards serve many purposes, and this leads to a variety of Tarot deck styles. Some decks exist primarily as artwork; art decks often contain only the 22 cards of the Major Arcana. Esoteric decks are often used in conjunction with the study of the Hermetic Qabala; in these decks the Major Arcana are illustrated in accordance with Qabalistic principles while the numbered suit cards (2 through 10) typically bear only stylized renderings of the suit symbol. In contrast, decks used for divination usually bear illustrated scenes on all cards. The more simply illustrated Marseilles style decks are used esoterically, for divination, and for game play.
The most popular deck today is probably the fully-illustrated deck confusingly known as the Rider-Waite-Smith, Waite-Smith, or simply the Rider deck. The images were painted by artist Pamela Colman Smith, to the instructions of academic and mystic Arthur Waite, and published by the Rider company. According to many accounts, Aleister Crowley also had substantial creative input. While the images are deceptively, almost childishly simple, the details and backgrounds hold a wealth of symbolism. The subjects remain close to the earliest decks, but usually have added detail. The chief aesthetic objection to this deck is the crude printing of colours in the original: several decks, such as the Universal Waite, simply copy the Smith line drawings, but with more sophisticated colouring.
Probably the most widely-used esoteric Tarot deck is Aleister Crowley's Thoth Tarot (pronounced tote). In contrast to the Thoth deck's colorful artistry, the illustrations on Paul Foster Case's B.O.T.A. Tarot deck are black line drawings on white cards; this is an unlaminated deck intended to be colored by its owner. Other esoteric decks include the Golden Dawn Tarot which is based on a deck by SL MacGregor Mathers, the Tree of Life Tarot whose cards are stark symbolic catalogs, and the Cosmic Tarot which is unusual for an esoteric deck because it is fully-illustrated.
The Marseilles style Tarot decks generally feature suit cards which look very much like modern playing cards. The numbered cards sport an arrangement of pips indicating the number and suit, while the court cards are often illustrated with two-dimensional drawings.
Other decks vary in their conventionality. Cat-lovers have the Tarot of the Cat People, a fairly standard deck complete with cat in every picture. The Tarot of the witches and Aquarian Tarot retain the conventional cards with varying designs. The witches deck became famous/notorious in the 1970s for its use in theJames Bond movie Live and Let Die.
Other decks change the cards partly or completely. The Motherpeace Tarot is notable for its circular cards and feminist angle: the mainly male characters have been replaced by females. The Tarot of Baseball has suits of bats, mitts, balls and bases; "coaches" and "MVPs" instead of Queens and Kings; and major arcana cards like "The Catcher", "The Rule Book" and "Batting a Thousand".
A very spiritual Tarot deck is the Isis Tarot also known as Tarot van Isis, Tarot d'Isis, etc., by Erna Droesbeke, using archetypical symbols.
Computing professionals might find the Silicon Valley Tarot most intelligible, which offers online readings. Major arcana cards include The Hacker, Flame War, The Layoff and The Garage; the suits are Networks, Cubicles, Disks and Hosts; the court cards CIO, Salesman, Marketeer and New Hire.