Players collect resources that enable them to rescue orangutans – but if you waste resources while doing so, you'll be punished at the end of the game.

To set up, shuffle the fifty-card deck (cards in five suits, numbered 1-10 in each suit), then deal each player ten cards. Shuffle the 16-card orangutan deck, then lay out 4 or 5 cards face up, depending on the number of players; each orangutan shows one or more suit cards on it, and a player must possess matching cards to claim that orangutan.

Each round, the lead player lays a card on the table, then each player follows, without regard for suit. Whoever played the highest card claims one card played by another player, then either places it on the table before her or uses it (possibly with cards collected earlier) to claim an orangutan. The player discards all cards needed to claim the orangutan, and tucks any remaining cards collected under that orangutan.

Each player must claim one card, if possible, adding it to her collected cards or claiming an orangutan. Discard any unclaimed card. After all players are finished, lay out new orangutan cards (if needed), then play another round.

Once players have played all ten cards in hand, the game ends. Each player sums the points on the orangutan cards she claimed, then loses one point for each excess card tucked or collected card still on the table. The player with the highest score wins.

Martin Wallace who produced the game is very kindly donating all profits from sales of Old Men of the Forest to the Orangutan Foundation.