There are numerous alternative rule sets for Pinochle. These variations accommodate different numbers of players and/or teams, number of cards in play and point values.
Two-handed Pinochle and three-handed Pinochle feature individual players, while four-handed Pinochle and higher feature pairs or teams. Double-deck Pinochle, as the name implies, is played with two Pinochle decks; this style of play is exclusively used by various Pinochle associations and tournaments, and is a popular format for online games. Double-deck Pinochle removes the nine cards from play.
Triple-deck, six handed Pinochle features two teams of three people playing with three decks of cards (the nines are removed from play). Double-deck Pinochle for eight players is similar to the four-handed format, but features four teams of two players each.
Gambling is commonly incorporated into many styles of Pinochle play and is often employed in sanctioned tournaments and online play.
The many styles of Pinochle play should be considered as baselines rather than ironclad rules; many players will establish their own variations. When participating in a game or tournament, it would be wise to familiarize yourself with that game's format and rules. Of course, as with all card games, inventive players often establish their own house rules.