There are currently about 17 million bitcoin in circulation. The emission of new bitcoin is not controlled by governmental institutions or central banks, as it is the case for traditional currencies, but is mathematically controlled by the technology itself and cannot be altered.
The emission model of bitcoin is scheduled to create new bitcoins about every 10 minutes, with a maximum quantity set at 21 million. As early as in 2035, more than 99% of the total amount of bitcoin will be issued.
It is therefore important to note than, differently than traditional currencies, whose emission can be altered by monetary politics, the emission of bitcoin is independent from political, social or economical motivations that can have an impact on the purchasing power of the currency. The future emission is, as mentioned, predetermined and cannot be altered. In addition, the number of bitcoin minted every 10 minutes gets halved every 4 years.