content: Bitcoin mining is the process by which transactions are verified and added to the public ledger, known as the block chain, and also the means through which new bitcoin are released. The mining process involves compiling recent transactions into blocks and trying to solve a computationally difficult puzzle.  The participant who first solves the puzzle gets to place the next block on the block chain and claim the rewards.  The rewards, which incentivize mining, are both the transaction fees associated with the transactions compiled in the block as well as newly released bitcoin.  The amount of new bitcoin released with each mined block is called the block reward.  The block reward is halved every 210,000 blocks, or roughly every 4 years.  The block reward started at 50 in 2009, is now 25 in 2014, and will continue to decrease.  This diminishing block reward will result in a total release of bitcoin that approaches 21 million.  - source  There's more info there, and on the google/alternative. Interesting note below.  Feb 1, 2017 - 80% of all Bitcoins Will Have Been Mined In a year From now ... the amount of bitcoins being mined every day is much compared to a few ... There is an estimate that it will reach 80% (or 16,800,000 coins) by the end of 2017.