Depending on how you look at it, our solar system has either eight planets or thirteen.
From the Sun outwards: Mercury, Venus, Earth, Mars, Ceres, Jupiter, Saturn, Uranus, Neptune, Pluto, Haumea, Makemake, and Eris.
When Eris was discovered the debate began (Nicknamed Xena at the time). And since Eris was found to be larger than Pluto, it was questionable whether Pluto was an actual planet, a Kuiper belt object or another new class of objects called a Plutoid. After some semantic wrangling, we were given the dwarf planets. Ceres was changed from being the largest asteroid while the nomenclature for Pluto was changed to what it is today.