Bitcoin is unique in that only 21 million bitcoins will ever be created. However, this is not a limitation at all, because bitcoins can be divided into smaller sub-units, such as bits - one bitcoin is equal to 1,000,000 bits. One bitcoin can be divided to 8 decimal places (0.000 000 01), and if the average single transaction size decreases to a certain extent in the future, it can be divided into even smaller units.