The 21st birthday is a strange paradox. The celebrated individual is clearly entrenched in adulthood, and yet the occasion is often seen as an opportunity to play silly games and drink plenty of alcohol. Therefore, a decent 21st birthday party will have an even balance of modest maturity and rampant silliness. Try a few adult games to reach that balance and make it a night to remember.

Twenty-first birthday parties often bring assorted individuals together who have never met. Therefore, a good icebreaker is in order. Write the names of famous celebrity couples on sticky notes--for instance, write "Brad Pitt" on one note and "Angelina Jolie" on another. When your guests arrive, give each guest a sticky note with the instructions to find his celebrity pairing. Use fictional couples if you run out of real celebrities. This game brings people together and offers an immediate topic of conversation.

After the icebreaker, announce the "No" party game, which takes place during the course of the evening. Each guest receives a clothespin and attempts to make other guests say the word "no." If a guest manages to trick another into doing so, the tricky guest wins her victim's clothespin. The guest with the most clothespins at the end of the evening wins a prize. To mix things up, allow the birthday person to win clothespins by making other guests say the word "yes." This game is sure to keep your guests on their toes.

Ask each party guest to write down three, six or nine nouns on small slips of paper, equally divided between people, places and objects. Fold all the slips and put them into a bowl. Split the group of guests into two even teams and have everyone sit in a circle. Moving around the circle, each player receives 45 seconds to pull out slips and describe the contents to teammates. Players cannot say any words written on the slip and cannot gesture. After all slips are used, replace the slips in the bowl for Round 2--each player can only use three words to describe each slip. Round 3 drops the word limit to one word per slip. This game conditions the group to associate single words with relatively complex nouns.

Most 21st birthday parties include drinking, especially by the celebrated individual since he is now "legal." As a drinking game, "Viking" requires all players to sit in a circle. The celebrant starts by holding his hands in the shape of Viking horns on his head. After a second or two, he claps his hands and points at another guest, who must make the Viking horns while the players to the left and right of the new Viking make rowing motions. The new Viking claps and points at another guest and the actions are repeated. Play continues in this manner until someone fails to perform the appropriate motion and takes a drink. The game can be played fast and requires focus and concentration.