This has become one of the most popular forms of poker, both in formal play and in home poker where it is the basis of numerous variants. Each player is dealt a seven-card hand, some of the cards being face up, with several betting rounds during the deal. At the showdown players use any five of their seven cards to make the best poker hand. Seven-card stud works well as a high-low game, and there is also a low only form known as Razz.
This page assumes some familiarity with the general rules and terminology of poker. See the poker rules page for an introduction to these, and the poker betting and poker hand ranking pages for further details.
A standard 52-pack is used and from 2 to 8 players can take part. The game is best for 5 to 7 players. When 8 play there is the problem that the cards may run out towards the end of the deal.
The sequence of events is as follows (as usual the cards are dealt clockwise one at a time):
The concealed cards - the first, second and seventh card dealt to each player - are sometimes known as "hole" cards.
Traditionally, each betting round is begun by the player with the best hand showing. For this purpose pairs, triplets, two pairs and quads count in their normal poker order - so for example with three cards showing 3-3-3 is higher than 7-7-8, which is higher than A-K-Q. Incomplete straights and flushes do not count. If there is a tie it is resolved by comparing the suits of the highest cards in the tied hands using the ranking order clubs (low), diamonds, hearts, spades (high).
Some play that in the first betting round (third street), the first player must place a compulsory bet, called the bring-in. In this case there may be no ante, though an ante is usually paid as well.
Some play that the first betting round starts with a compulsory (bring-in) bet by the player showing the lowest card. This is now the normal rule in formal games hosted by American casinos. The subsequent betting rounds from fourth street onwards are begun by the highest hand showing as usual.
This is of course for the players to agree. Seven Card Stud is often played as a fixed limit game with the following arrangements.
If there are eight players and after sixth street no one has folded, there will not be enough cards to deal everyone a seventh card. In this case a single "community" card is dealt face up to the table and this counts as everyone's seventh card. Everyone then effectively has five cards showing, including the community card, and seventh street betting is begun by the player for whom this makes the highest poker hand - straights and flushes not count. Ties are resolved by the suit of the highest card as usual.
In formal games it is usual for the dealer to "burn" one card - placing the top card of the deck face down under the pot - at each stage of the deal. In this case the card can run out even with only seven players. If the dealer determines that there are not enough cards to complete the deal, the burned cards are retrieved from under the pot and shuffled with the remains of the deck, and if possible a card is then dealt to each player.
Note that in no case are cards discarded by a player who has folded returned to the deck to be dealt. These cards are dead.
The deal and betting are mostly the same as in ordinary seven card stud. Some play that in high-low games, a pair showing does not give players the option of a big bet or raise.
At the showdown, each player selects five cards to make a high hand and five possibly different cards to make a low hand. The pot is split equally between the highest and lowest hands, the odd chip going to the high hand if the amount cannot be divided exactly by two. Any of the possible low hand ranking methods can be used - see low hand ranking on the poker hand ranking page.
Since different selections of cards can be used for the high and low hands, it is entirely possible for one player to win both halves of the pot.
In formal games, the rule is that "the cards speak for themselves". That is - at the showdown each player is entitled to compete with the highest and lowest hand that can be made from his or her seven cards, even if the player does not correctly identify the best selections of five cards.
In formal games there is often a qualification rule that a low hand cannot contain any card higher than an 8. In this case the ace-to-five system of low hand ranking is used. This variant is called Seven Card Stud Hi-Lo Eight or Better, often abbreviated to Seven-Stud/8. If none of the players has a qualifying low hand at the showdown, the high hand wins the whole pot.
In home games, Seven Card Stud High-Low is often played with declaration. After the seventh street betting round each player has to declare either "high", "low" or "both". This can be done either in sequence around the table or simultaneously. In the simultaneous method each player holds out a closed fist containing one chip for "high", no chips for "low" or two chips for "both", and when all are ready, everyone reveals their choice.
In the showdown, if no one declared "both", the highest hand among the players who have declared "high" shares the pot with the lowest of the players who have declared "low". If all declare "high" or all declare "low", the winner takes the whole pot. A player who declared "both" has to have the highest hand or all the "high" and "both" players and the lowest hand of all the "both" and "low" players to win the whole pot. A "both" player who loses or ties either high or low cannot win any part of the pot.
See the sections on declaration methods and the showdown in split pot games on the poker betting page for further details and variations.
Razz is seven card stud played for low only, using ace-to-five ranking (see hand ranking in low poker). In the first betting round the compulsory bring-in bet is made by the owner of the highest card showing. In subsequent rounds, from fourth street onwards, the lowest hand showing bets first. Ace is low and king high throughout, and as usual the suit of the highest card is used to break ties, so if on fourth street two players tie for lowest with 
6-
2 and 6-
2 the second hand will start the betting, because the six of clubs is lower than the diamond.
In fixed limit games the limits double at fifth street: on third and fourth street only small bets are allowed, and from fifth street onwards only big bets. Pairs showing have no effect on the size of bets.
The RAZZ page of the Play Lowball Poker site has further information on the history and variants of this game.
London Lowball is seven card stud played for low only, using ace-to-six ranking (see hand ranking in low poker).
Normally a pot limit betting structure is used (see betting limits).
In home poker, seven card stud is often played with wild cards, which of course increases the frequency of the higher hand types. In the simplest case the wild cards can be all cards of a certain rank, as agreed by the players or specified by the dealer in a dealer's choice game - for example seven card stud, deuces wild. The game with wild cards can of course also be played high-low or low only.
There are also some more elaborate seven-card stud variants in which the wild cards are determined by the players' cards in the course of the deal.
This game, also known as Late Show, is seven card stud in which each player's lowest concealed card is wild for that player only. That means for example that if your first three cards are 
9-4 face down and 3 face up, all your fours will be wild unless your seventh card, which will also be face down, is a 3 or a 2, making that rank wild instead.
Low Hole is normally played as a high game, but can also be played low or high-low. In the case of high-low, if you use ace-to-six or ace-to-five ranking of low hands, then an ace in the hole will make aces wild for the purpose of low hands but not for high hands.
Six players are the maximum for this variant, in which players can improve their hands by substituting cards.
Deal, play and betting are the same as in seven-card stud up to the point where each player has five cards (two down and three up). After the subsequent betting round and before the sixth card is dealt, each player in turn, starting with the player to dealer's left, has the option to exchange any one card. The player may either discard a down card and be dealt a new down card or discard an up card and be dealt a new up card, or choose to stand pat and not exchange any card. Then a sixth card is dealt to each player face up, there is a betting round and another round of exchanging. There is a final betting round followed by a showdown.
If there are five or fewer players, a seventh face-down card can be dealt, as in seven-card stud.
Some set a price for exchanging, which may be equal to the minimum bet at that point. In this case, anyone who exchanges must pay that amount to the pot. This does not count as a bet and does not have to be matched by the other players.
Brian Johnson describes this game, in which each player is dealt six cards and there is a joker in the centre of the table that acts as everyone's seventh card. The joker is not fully wild, but functions rather like the "bug" in 5-card draw. It can represent an ace, or a card needed to complete a player's straight or flush, but cannot be used to form a set of equal cards other than aces. Deal and betting are the same as in seven-card stud up to the point where each player has five cards (two down and three up). After the ensuing betting round each player gets one last face down card and there is a final betting round.