Insurance is an option that lets you place a side-bet of up to half of your original bet when the dealers deal himself an Ace. If the dealer will have a blackjack after his hidden card is revealed, you will get paid on a ration of 2:1 for your side bet and your original/initial bet will be taken. If he does not have a blackjack, you will loose your side bet, but notice that you might as well lose your original bet as well if the dealer's hand beats yours.
If the dealer up card is an Ace then after the cards are dealt and no further actions were made the dealer would simply ask "Insurance?", if a player would choose this option he would then need to place a sum as high as half of his inital bet on the specific place on the table for insurance bets.
After all insurances bets are placed the dealer would then have a look at his down-card, if he has a 10 value card such as a Jack or Queen then the game take no further steps, the money insurances bets would be paid and the initial bets placed by players would be taken away by the dealer.
A player may have a blackjack at the same time that a dealer's up card is an Ace and in such occasions the dealer would offer "even money". This option is only presented when a player has a blackjack and it is identical to the regular insurance in the final calculation whether the dealer had a ten in his hole card or not..
While some players find this type of insurance a bit odd with a simple example you can see how simple it is: If a player puts insurance while he has a blackjack on an inital $20 bet and the dealer's got a blackjack - he then wins the insurance money - $20 for a $10 insurance, and his inital bet is saved since it's a push - net profit of $20. If the dealer's didn't had a ten in his hole card then the player would lose his insurance money - 10$ - but would win the bet and get paid 3:2 - $30. $30-$10= net profit of $20. In the end and insurance is equal to the "even money" option.
To conclude: The chances for the dealer to have a blackjack are bigger, and in most casinos if the dealer gets a blackjack you automatically loose even before you had the chance to play, unless you get a blackjack yourself as well and than its a "push" which means no one wins the round, so it's preferable that would place an insurance if you feel that the dealer's down card is a ten.
Article contributed by Sam Marshall 30th of november '05