The main region of the 4th Generation of Pokemon, and the games Pokemon Diamond, Pearl and Platinum. With the addition of the large island to the north east, and the area that can be accessed from the eastern side of Victory Road, the Sinnoh region is home to more Pokemon species than any other.
A main feature of Sinnoh is Mount Crornet where depending what game you playing is where Diagla, Palkia, or Giratina lives.
Sinnoh was the first region shown in the Pokemon games to possess snow. This was later replicated in the Generation V region of Unova.