Players compete to empty their hands by discarding cards to represent selling horses. On each turn, a player either plays a card matching the horse breed of last discarded card, or plays a "directional card" to change which breed is being played. If the player cannot play a card, she instead draws one from the deck.
In the words of the publisher, "WHOA! is a game of challenge in the marketplace. How many different breeds of horses have you owned over the years? Here's a chance to own more (without the expense) before you finally sell your entire herd. Be the first horseman to do that, and and you win the game of WHOA!"
Like Uno, WHOA! is a commercial version of Crazy Eights, a public domain card game played with a standard deck of playing cards.