* Carbon-12 (¹²C): This is the most abundant isotope of carbon, making up about 98.9% of all carbon found in nature. It has 6 protons and 6 neutrons in its nucleus.

* Carbon-13 (¹³C): This isotope is less abundant, making up about 1.1% of naturally occurring carbon. It has 6 protons and 7 neutrons in its nucleus.

There is also a third, less abundant isotope:

* Carbon-14 (¹⁴C): This is a radioactive isotope with 6 protons and 8 neutrons. It is used for radiocarbon dating, a method to determine the age of organic materials.

It's important to note that all carbon isotopes have the same number of protons (6), which determines their atomic number and defines them as carbon. The difference lies in the number of neutrons they have.