Unlike conventional currencies, Bitcoin's supply is limited to 21,000,000 BTC. Currently, there are 18,286,025 BTC in circulation (data as of March 25, 2020).
The Bitcoin price depends on its supply and market demand. The greater the demand, the higher its price, and vice versa.
The Bitcoin price may also be influenced by the cost of its production, also known as mining costs. Some other factors may have an impact on the value of Bitcoin too. These may include official announcements regarding Bitcoin regulation, the increasing number of cryptocurrencies that attempt to rival Bitcoin, the number of exchanges where Bitcoin is listed, and some other factors.