Bitcoins are created as rewards granted to miners for solving blocks in the Bitcoin blockchain, thereby ensuring its security. When Bitcoin was created, it was written into its protocol that the supply of Bitcoin would be restricted to 21 million. Every 210,000 blocks that get mined, the rewards are halved. This means that the last Bitcoin won’t be mined until roughly 2140.

At this point, there will never be any more Bitcoin issued into circulation, unless the Bitcoin software is changed, which is highly unlikely. When the last Bitcoin is mined, miners will no longer be awarded new Bitcoin for verifying and securing transactions