As of 2014, there are 15 isotopes of carbon. They are C-8 through C-22. Only C-12 and C-13 are stable, while the other isotopes are radioactive, and of these, only C-14 is found in nature.
C-14 is famous for its use in carbon dating and has a half-life of 5,700 years. This means after 5,700 years, half of the carbon will have decayed into nitrogen-14.
C-11 is the most stable of the man-made isotopes, with a half-life of a little over 20 minutes. The other radioisotopes have half-lives that last for seconds or fractions of seconds. C-13 is used in research and medicine, and C-12 is used to establish the atomic weight of other isotopes.