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 four years. The block reward started at 50 bitcoin in 2009, and is now 25 bitcoin in 2014. This diminishing block reward will result in a total release of bitcoin that approaches 21 million. According to current Bitcoin protocol, 21 million is the cap and no more will be mined after that number has been attained.
As of today, block rewards provide the vast majority of the incentive for miners. At the time of writing, for the previous 24 hours, transaction fees represented 0.3% of mining revenue.