What will happen once all Bitcoin are mined?

Bitcoin is created through a process called mining. Using supercomputers, these miners confirm transactions on the Bitcoin blockchain and are rewarded for their efforts in the form of newly-created Bitcoin. These payments are called block rewards. 

Through a process called halving, block rewards will continue to be halved at a determined rate until there are 21 million Bitcoin in circulation. When this happens, sometime around the year 2140, no new coins will be created ever again. After this milestone is reached, the miners will be paid in transaction fees.