The word "improvise" is derived from the Latin word improvisus meaning "not foreseen." In improvisational theater or improv, the actors do not use scripts, rendering worry about mistakes unnecessary. Of course, that means there is no script to rely on for support, nothing to tell an actor what comes next. The unforeseen, the not knowing what will happen next, makes improv so compelling and unique. It also makes improv difficult to fully describe and illustrate.
Imagine a world where fear doesn't exist, where danger is something you run toward instead of away. In this world, adults return to their childhood and play make-believe. The whole point of this world is to have fun, take chances and possibly fail. In this world, if you are not actively pursuing the danger of failing, then you're not playing right. Asaf Ronen, author of "Directing Improv: Show the way by Getting Out of the Way" says, "improv audiences want to see you have fun or be at risk."
Improvisers make everything up as they go along, often with hilarious results, but they do not reinvent the wheel. There are strategies, rules and techniques that improvisers use, but improvisers don't waste time analyzing techniques or conducting scholarly research. Improvisers play games! Improvisers want to have fun! Shana Merlin, of Merlin-Works Institute for Improvisation teaches that the most important rule to follow is to have fun. "Because fun is fun and that's the whole point."
Improv games can be loosely divided into two categories, Performance and Non-Performance games. Non-Performance games are fun to play, but may not be entertaining to for an audience to watch. The games can foster teamwork, encourage spontaneity or act as an ice breaker. "Woosh, Bang, Pow is a good example of a warm-up game. It is a simple game where a group of people stand in a circle and pretend to pass an imaginary ball around the circle. Players can "Woosh" the ball to the next player, "Bang" it back the way it came, or "Pow" it across the circle to a completely different player. The faster the "ball" moves, the more risk there is for messing up the pattern which means there is more fun.
Performance games are fun to play and entertaining to watch. A good example is "Category Die. In this game all the improvisers gather in a semi-circle in front of the director. The director gets a suggestion for a category from the audience, like breakfast cereals. Then the director points at each player. The player has to name a breakfast cereal without hesitation or repeating one that has gone before. The audience shouts out "DIE" when a player makes a mistake and then that player is out.
One performer described improvisation as "the most dangerous art form known to man." Tight rope walkers and sword swallowers probably wouldn't agree, but anyone that gets nervous at the prospect of delivering a written speech to an audience can appreciate the sentiment. No safety nets, no scripts, little or no props to speak of. Del Close, a prominent improviser, said that improvising is when you "fall and figure out why on the way down."