Variations by Player Count
Euchre is a four-player partnership game, but it adapts. The common adaptation is three-handed Cutthroat, which keeps the trick-taking and the bidding and drops the fixed partnership.
Standard (Four-Player)
Two teams of two, sitting across from each other. Each hand one team names trump and must take at least three of the five tricks to score, and the first team to 10 points wins. Documented in full on the euchre rules page.
Cutthroat (Three-Player)
No partners. Each hand the player who calls trump plays alone against the other two, who defend together for that hand only. Calling is tighter than in the partnership game, not looser: you need three tricks with nobody to supply one, so the hands that are worth a call are a clear step stronger. The full page covers the deal, the dealer pickup that matters more here than at four, scoring (including where tables disagree on the march and euchre payouts), and strategy for calling and defending.
Bidding Modifications
These change how trump gets chosen, usually to kill the dead hand that results when everyone passes through both rounds.
Stick the Dealer
If the second round reaches the dealer with nothing named, the dealer cannot pass and has to name a suit whatever they are holding. No hand is ever thrown in, and a small positional disadvantage lands on whoever is dealing. The full page covers the mechanics, which way each seat's bidding shifts, and what to name when you are the one stuck.
Weak-Hand Rules
These do something about a hand too weak to play. The two set different thresholds, and many tables run both.
Ace No Face
A hand holding exactly one ace and four cards below the Jack is thrown in and dealt again by the same dealer. The hand is technically playable, which is why the rule has genuine detractors. The full page covers what qualifies, how often it comes up, and the argument on both sides.
Farmer's Hand
A hand of nothing but 9s and 10s, with no ace and no face card, is thrown in and dealt again by the same dealer. The most widely accepted of the two, and the rarest trigger, at roughly one deal in 759. Tables that would rather keep the deal can switch on Going Under instead, which has that player give up three cards for the three undealt ones. The full page covers both forms, the looser thresholds other tables use, and how often each comes up.
Scoring Modifications
These leave the deal and the bidding alone and change only what it takes to finish.
Must Win by 2
Reaching the target score wins the game only if you are also two points clear. At 10–9 the game is not over: play carries on, and 11–10 does not end it either, until one side is both at the target and two ahead. It is the deuce rule from tennis, borrowed. The practical effect is a longer game at the end of a close one, and it is worth knowing the direction it pushes your bidding: trailing by one at 9–10 you are no longer playing for a single point to steal the game, because a single point only draws you level, so the marginal call that would have been enough under normal scoring is not.
In Cutthroat the gap is measured against whichever of the other two players is higher, which makes the rule bite harder: a euchre pays two to each defender there, so both of them can cross the target on the same hand and still have nobody two clear.
Combining Rules
They stack. Stick the Dealer solves passed-out hands, and the weak-hand rules solve dealt-but-weak ones, so the two categories never collide. Must Win by 2 touches neither, since it only reads the scoreboard. All four work in Cutthroat without modification.