Solitaire is a centuries-old, traditionally one-player card game that has entertained millions of people. Most people have played a game of "regular" Solitaire, otherwise know as Klondike Solitaire. Two-Handed Solitaire (otherwise known as Double Solitaire) is a similar game that builds on the traditional rules and allows for another player. This makes it a more social, fast-paced game, and potentially more entertaining than the original.
Shuffle each deck separately, then give each player a deck to deal as if he were playing a regular game of Solitaire. This means that there are seven piles: The leftmost will be a single face-up card; the next will have one card face-down and a second face-up card on top; the third pile will have two cards face-down and one face-up, etc., until completing the rightmost pile of six cards face-down and one faceup. Leave enough space between the two players' stacks to place other cards between. Each player will then keep his remaining cards in a stack face-down to play with.
Determine who takes the first turn based on the lower-numbered card in each leftmost pile. If there's a tie, decide by the lower card in the next pile over. Player 1 plays his hand just as in Klondike Solitaire; Place aces face-up in the space between the two players' layouts or above and build cards of the same suit in ascending order onto the aces. Cards can be moved around on your own layout, but not your opponent's. Use your stack of 24 face-down cards to add cards to your layout. Player 1's turn ends when he can no longer make any moves.
When the Player 1 can no longer make moves, it's Player 2's turn. She will also play as if playing Klondike, with one exception: Both players can now place cards on the either players' stacks of aces. When Player 2 has no more moves, it's Player 1's turn again. Play passes like this throughout the game.
The game ends when either one player wins by playing all of his cards or neither player can make any moves. In the case of neither playing having any remaining moves, the player who has played the most cards to the aces stacks wins.