Card counting is one of those topics that has entered pop culture on some level with movies like 21 becoming popular. Even though a lot of people know that it has something to do with keeping up with the cards in blackjack, the majority of them don't really understand why or how it works. Without understanding the mechanics of why card counting works how it does, a player is pretty much hopeless to learn how to implement a card counting system as a part of an overall blackjack approach that includes basic strategy and other elements.

In a deck or shoe of cards in a blackjack game, not all cards are worth the same amount to you. Because of the rules of how the dealer has to hit in certain situations and how blackjack gives you a higher payout than normal, you have a big advantage when there are a lot of tens and aces in the deck compared to other cards. What you would love to have happen is that the deck be mostly full of these cards, and that would be a fantasy scenario where you could have an enormous advantage over the house with correct play.

The way the deck or shoe is manipulated in blackjack is that cards are dealt from it. When a lot of low cards are removed from the deck, a situation is created where you have a nice advantage. However, if several high cards are taken from the deck, you're put in a spot where it will basically be impossible for you to even come close to getting an advantage, and you will often be better off just leaving the table completely. Keeping up with a ratio of high cards and low cards left in the deck is the basic idea that drives card counting.

So how does it work? All of the cards are given a score, and you add or subtract their score from a running count as they are dealt. Different cards are scored differently depending on which counting system you're using, but high cards are usually given negative values while low cards are given positive values. With this convention, when the count reaches a high number, you have an advantage. Along the same lines, when it gets very low, then you know that the house has a larger advantage than average.