Bitcoin’s monetary policy follows a fixed schedule, which is regulated by the Bitcoin protocol software itself. What this means is that new bitcoins can only be created during the mining process via the block subsidy. The specific amount that is created diminishes over time. Every 210,000 blocks, the number of bitcoins generated per block decreases by 50% in an event called the halvening.
The total supply of Bitcoin is finite. Only 21 million bitcoins will ever exist. With the current issuance rates and halvening schedule, the last bitcoin will be mined sometime in 2140.